Need some js help with my form

Hey everyone, I am creating a simple form (see code below), and I need some help with some of the javascript components (I am new to javascript):

  1. The second question on my form asks the user to “select one or more crops”. I need to assign a variable to each of the three choices (corn, soybean, and wheat), so the names of the crops that the user chooses can be used in the third question (“select one or more climate regions for $crop1”) and possibly the 5th question (“for $crop2, are the climate regions the same?”).

  2. If the user selects more than one crop, the form should display a 5th question that asks (“for $crop2” are the climate regions the same?"). If they only choose one crop, no 5th question should be displayed.

If anyone has some extra time to help me with this it would be much appreciated. Thanks.

<body>
            <form action="" method="post" class="AdvancedForm" name="WeedSurvey">
                <table cellpadding="3" cellspacing="2">
                	<tr>
                        <td>
                            Select a state:
                        </td>
                        <td>
                            <select name="ValidSelection" id="ValidSelection" onchange = "showImage(this.value)">
                                <option value="00images/defaultImage.gif" selected="selected">Select a State</option>
                                <option value="08images/alabama.gif">Alabama</option> 
                                <option value="07images/arizona.gif">Arizona</option> 
                                <option value="09images/arkansas.gif">Arkansas</option> 
                                <option value="07images/california.gif">California</option> 
                                <option value="05images/colorado.gif">Colorado</option> 
                                <option value="03images/connecticut.gif">Connecticut</option> 
                                <option value="02images/delaware.gif">Delaware</option>  
                                <option value="07images/florida.gif">Florida</option> 
                                <option value="09images/georgia.gif">Georgia</option> 
                                <option value="10images/idaho.gif">Idaho</option> 
                                <option value="09images/illinois.gif">Illinois</option> 
                                <option value="09images/indiana.gif">Indiana</option> 
                                <option value="09images/iowa.gif">Iowa</option> 
                                <option value="09images/kansas.gif">Kansas</option> 
                                <option value="04images/kentucky.gif">Kentucky</option> 
                                <option value="09images/louisiana.gif">Louisiana</option> 
                                <option value="03images/maine.gif">Maine</option> 
                                <option value="08images/maryland.gif">Maryland</option> 
                                <option value="03images/massachusetts.gif">Massachusetts</option> 
                                <option value="10images/michigan.gif">Michigan</option> 
                                <option value="09images/minnesota.gif">Minnesota</option> 
                                <option value="10images/mississippi.gif">Mississippi</option> 
                                <option value="06images/missouri.gif">Missouri</option> 
                                <option value="07images/montana.gif">Montana</option> 
                                <option value="09images/nebraska.gif">Nebraska</option> 
                                <option value="04images/nevada.gif">Nevada</option> 
                                <option value="02images/new_hampshire.gif">New Hampshire</option> 
                                <option value="03images/new_jersey.gif">New Jersey</option> 
                                <option value="08images/new_mexico.gif">New Mexico</option> 
                                <option value="10images/new_york.gif">New York</option> 
                                <option value="08images/north_carolina.gif">North Carolina</option> 
                                <option value="09images/north_dakota.gif">North Dakota</option> 
                                <option value="10images/ohio.gif">Ohio</option> 
                                <option value="09images/oklahoma.gif">Oklahoma</option> 
                                <option value="09images/oregon.gif">Oregon</option> 
                                <option value="10images/pennsylvania.gif">Pennsylvania</option> 
                                <option value="01images/rhode_island.gif">Rhode Island</option> 
                                <option value="07images/south_carolina.gif">South Carolina</option> 
                                <option value="09images/south_dakota.gif">South Dakota</option> 
                                <option value="04images/tennessee.gif">Tennessee</option> 
                                <option value="10images/texas.gif">Texas</option> 
                                <option value="07images/utah.gif">Utah</option> 
                                <option value="03images/vermont.gif">Vermont</option> 
                                <option value="06images/virginia.gif">Virginia</option> 
                                <option value="10images/washington.gif">Washington</option> 
                                <option value="06images/west_virginia.gif">West Virginia</option> 
                                <option value="09images/wisconsin.gif">Wisconsin</option> 
                                <option value="10images/wyoming.gif">Wyoming</option>
                            </select>
                        </td>
                    </tr>
                    <tr>
                        <td>
                            Select one or more crops:
                        </td>
                        <td>
                            <span id="ValidCheckbox" class="InputGroup">
                                <label for="ValidCheckbox_1">
                                    <input type="checkbox" name="ValidCheckbox" id="ValidCheckbox_1" value="Corn" />Corn
                                </label>
                                <br/>
                                <label for="ValidCheckbox_2">
                                    <input type="checkbox" name="ValidCheckbox" id="ValidCheckbox_2" value="Soybean" />Soybean
                                </label>
                                <br/>
                                <label for="ValidCheckbox_3">
                                    <input type="checkbox" name="ValidCheckbox" id="ValidCheckbox_3" value="Wheat" />Wheat
                                </label>
                                <br/>
                            </span>
                        </td>
                    </tr>
                    <tr>
                        <td>
                            Select one or more climate regions for $crop1:<br />
                            <span ><img src = "images/defaultImage.gif" id = "theImage"></span>
                        </td>
                        <td>
                        	<span id="ValidCheckbox2" class="InputGroup">
                        		
                            </span>
                        </td>
                    </tr>
                    <tr>
                        <td>
                            Drag and drop app
                        </td>
                        <td>
                            
                        </td>
                    </tr>
                    <tr>
                        <td>
                            For $crop2 are the climate regions the same?
                        </td>
                        <td>
                            <span id="ValidRadio" class="InputGroup">
                                <label for="ValidRadio_1">
                                    <input type="radio" name="ValidRadio" id="ValidRadio_1" value="Yes" />Yes
                                </label>
                                <br/>
                                <label for="ValidRadio_2">
                                    <input type="radio" name="ValidRadio" id="ValidRadio_2" value="No" />No
                                </label>
                            </span>
                        </td>
                    </tr>
                    <tr>
                        <td>
                        </td>
                        <td>
                            <input type="submit" value="Submit" id="FormSubmit" style="background: #EFEFEF;"/>
                        </td>
                    </tr>
                </table>
            </form>
            
			<script type = "text/javascript">
			function showImage(which) {
			var numBoxes = parseInt(which.substring(0,2),10);  //NB must be decimal!!
			s = which.substring(2,99);
			document.getElementById("theImage").src = s;
			var content = "";
			for (var i = 1; i <= numBoxes; i++) {
			content += "<label for='ValidCheckbox_01'><input type = 'checkbox' name = 'ValidCheckbox2' id= 'ValidCheckbox_01' value= '1'>" + i + "</label><br />"  <!--
			//"ValidCheckbox_01 needs to add for each label (i.e. 01, 02, etc...), need to ad value for input that adds as well (i.e. 1,2,3, 	etc.)-->
			}
			document.getElementById("ValidCheckbox2").innerHTML = content;
			}
			
			</script>

    </body>