This is what I would do
?>
<tr class="nav" onMouseOver="this.className='mainnavhilite';" onMouseOut="this.className='mainnav';" onClick="self.location='<?php echo "$menu_url?menu=$menu_id&page_id=$page_id"; ?>'"><td class="mainnav"><?php echo "$menu_text"; ?></a><br /></td></tr>
So rather than use echo to output your javascript, it's better to exit out of php mode, then go back into php whenever you need to.
Richie.
geocities.com/akindele/