Taken from a post I answered last week.
Go to admin cp open styles and templates, then style manager, find forumrules template for the style you want to remove it from... then highlight the whole template and delete it and save.
gone like magic, LOL
Or... you can remove
Code:
<td width="100%" valign="top">
$forumrules
</td>
from your showthread and/or forumdisplay. In case its good for one page but not the other.