Choosing submit button with javascript

[gex6]

I have a form with the following drop down

 <select name="option" onChange="nav(this);">
 <option value="">----------------</option>
 <option value="copyfile">Copy</option>
 <option value="renamefile">Rename</option>
 ......yadda yadda.....
 </select>

Im wanting a certain submit a certain input button (I have several different ones in one form) depending on which drop down item they select.

So if they select Copy. I would want the javascript function to basically act like <input type="submit" name="copyfile" /> was clicked, and similarly if Rename was clicked, I would like it to act as if <input type="submit" name="rename" /> was submitted.

Thanks,
gex6

[reminder]

function nav(obj) {
switch(obj.options[obj.selectedIndex].value == "bla") {
case "bla": alert("bla"); break;
case "blabla": alert("blabla"); break,
}
}

cheers