What browser are you using? Presumably some version of IE since this is caused by your browser having a bugged box model. If you're using IE6 try upgrading to IE7, it supposedly has much better (although still flawed) standards support.
I'm using IE7. And apparently it's a width issue for div.
Krejt, if you can find where that side box is located (the one where the names are) in the style sheets, the best thing would probably be to set a fixed width that isn't too big instead of a percent width. If that doesn't work, then I'm not sure. I've only edited PHPBB forum coding, so I don't know anything about UBB coding.
