ah yes, I stand corrected, I didn't bother looking at the form! the ID is also not a hidden field being sent to the edit script, either.

so, if that's the issue, you can either make the form post to "edit.php?id=$_GET['id']", or add a hidden input that holds the ID, and then access it with $_POST['id'].
Code:
<input type="hidden" name="id" value="<?php echo $_GET['id']; ?>" />