Alright, for ages I've wondered how Extremepixel made borders on their skins, like this (http://www.bellegerent-designs.com/forums/) one for example. I'm wondering, do I need to add it as an extra CSS item? If so, how?

Am I on the wrong track? Please explain if any of you know :)

you talking about the left and right border ?
If so those are images and not css =)

Nah, I discovered how recently, but the boards I co-admin on have been having DB issues lately and I can't get into the ADmin CP to test my newly aquired knowledge. ;)