Special "ads" for specific users

I want to know if anyone can help me with this. I don't even know if it's possible.

I want to be able to have ads for let's say moderators. So when they are logged on to the forum they can se ads like "Special offer for moderators" as an image on the site. But I want to use it outside the forum, but use the same session (or whats used). Anyone know how I can do this?

Little like this: (just to explain)

If moderator: show this ad
moderatorads.gif
else
regularuser.gif