[Sean S]

edit the templates that contain the adsense code and add an if condition, probably the easiest way to do,

<if condition="$forum[forumid] == X">
		&nbsp;
	<else />
		place adsense code here
</if>

just replace X with the id of the forum that you don't want the ads to be displayed. Another thing you can do is to create a new style without the ads, and set that style as the default style for that forum.