Form Validation - Prevent Certain Buttons Firing

I have a general form validation question. I know very little about
javascript, a little more about PHP. Using yav (http://yav.sourceforge.net):

<form method="POST" name=edit onsubmit="return performCheck('edit', rules,
'classic');" action="pages_edit_submit.php">
<input type="text" name="title">
<input type="submit" name="Save">
<input type="submit" name="Cancel">
</form>

.... PerformCheck fires when any submit button is click, which is logical but
I'd like to prevent this if it was the cancel button that was clicked (and
preserve form submission on pressing Enter whilst in the 'title' box.