Help with my VBulletin Issue?

Hi all, I’m having a sizing problem with my vBulletin forum.

http://www.b2bypm.com/forum/

That’s how it should look, but if you click main forum, then click new thread, you’ll see that it is too wide for my design and therefore messes up what i have created.

Does anybody know how to fix this?

Thanks!

Ben :skull: