How do I change javascript action from Submit to ImageField?

Hello, I found this free script that I want to use on my order form (disables order button until agreed to terms by clicking checkbox). It is working, but I would like to use an image.gif-button instead of a Submit-button.

Would be grateful if someone could explain how to change in the script from “disable Submit-button”-action to “disable image.gif-button”-action. I’ve tried to do it myself, but I don’t know much about Javascript, and couldn’t get it to work.

My 2nd question: Can this type of action only be done in Javascript, or could there be a solution whereby the checkbox on the html-page calls a php-page to get the same type of validation?

Thank you

The script:
[COLOR=“Blue”]<head>
<meta http-equiv=“Content-Type” content=“text/html; charset=iso-8859-1” />
<title>Checkbox Form Validation</title>
<script type=“text/javascript”>

function AuthorizeValidation(myform) {

if(myform.iagree.checked == true) {myform.validation.disabled = false }

if(myform.iagree.checked == false) {myform.validation.disabled = true }

}

</script>

</head>
<body>
<form action=“” method=“post” name=“myform”>

<p><input type=“checkbox” name=“iagree” value=“valeur” onClick=“AuthorizeValidation(this.form)” /> I agree with general terms and conditions</p>

<p><input type=“submit” name=“validation” value=“Order” disabled /></p>

</form>

</body>
</html>[/COLOR]

[COLOR=black]Change this

<p><input type="submit" name="validation" value="Order" disabled /></p>

to this

[/COLOR]

<p><input type="image" src="path/to/url" name="validation" value="Order" disabled /></p>

Thanks!
How do I add a link to this?
I tried to by adding an a href= either before or after the disabled/>, but it doesn’t work.