Fabian,
Yes, there is a problem in your code. I'm sorry you misunderstood me. Your code needs to look like this:
Code:
<!-- Site Supporter Code -->
<if condition="$post[usergroupid] == 2 and is_member_of($post, 9)"><img src="images/misc/supporter.gif"></if>
<!-- / Site Supporter Code -->
you were supposed to take the words 'PRIMARYid' and 'ADDITIONALid' and substitute them out with the actual ID #'s.
I hope this clears up any confusion for you.