Changing the forum icons?

[Llandy]

Hi

I got a question which I've tried to google myself through, but without any luck. I'm trying to figure out how to change the icons which shows new threads, no new threads and closed threads to completely individual icons instead. Like these guys have: http://www.realitymod.com/forum/

I'm clueless as of where to find the answers for this and I've spent the last hour trying to find it on google. Any answer as how to do this would be much appreciated.

Thanks