You should be able to do something like this in JavaScript to clear a form element.
Code:
document.getElementById('formElementID').value = '';
There's probably easier ways to do it to all form elements.. but I'd have to look it up.
If you want a button that clears or resets a form, you could just use :
Code:
<input type="reset" name="reset" value="reset" />
This resets a form to it's initial state on the page load.