Replace '$vbphrase[reply_rule' in the templates 'showthread_quickreply' and 'newreply' with this:
Code:
<table style="width:100%;" cellpadding="0" cellspacing="0" border="0"><tr><td class="important">IMPORTANT:</td><td class="redtable">
<span class="smallfont"><strong>$vbphrase[reply_rule]</strong></span></td></tr></table>
Also, be sure to add the CSS Selector (for importand and redtable) in your All Style Options Page.