Need help with fixdth width

[Zellbet]

I'm not sure if this goes here or if anyone here can help. But on my site Zellbet.com (http://www.zellbet.com). The main portal works fine, but on the forums, the width goes crazy. Some pages it's fine but other are terrible. If anyone can give me a example to how to fix this, I would be gratfull. As i am not so good with html. here is a example of how the pages are differnet.

http://www.zellbet.com/forums/showthread.php?t=9