small icon or image for certain usergroup under username
 

What to do, and how to hack this, so I could place a small icon for my user's group instead of the group with text under the username.

and only for one special group.

thank you:)

Check out User Ranks

thanks.. by the way, what is the difference between rank and title.. ??

They get shown in different places. Also, some sites like to allow their users to have personal titles, so you don't want to use titles to do this if that is the case. Also, usually titles are just text, not images. And, titles get applied to all usergroups, whereas with ranks, you may apply them to just certain usergroups. You can read up on both in the manual I linked you to.