Image in postbit based on group membership

[RustedBucket]

Hi. I'm thinking this should be really simple but it's not working quite right for me. I have a secondary group that I want to display an image for in the thread postbit if a user is a member of that secondary group. I'd like it to be visible to everyone viewing the thread.

secondary group: testgroup
image: testimage.gif

Can someone write me a quick conditional to do this. I'm guessing it can be done with a template conditional but everytime I try I get nothing or everyone gets the image.

Thanks

[amykhar]

The conditional is
<if condition="is_member_of($post,testgroupidhere)">

[RustedBucket]

Thanks Amy, one mroe stupid question, what does $post signify?

[amykhar]

It holds all the data in the post. The user name of the poster, userid, the message, everything.

[RustedBucket]

Cool.. thanks for that. Worked like a champ.

[davew]

Thanks Amy... I'd spent hours trying to get this to work properly :)