Width of the forums

I'm new and I just installed my punbb forums, so far it is AMAZING. However, the rest of my site is centered at a width of 600 pixels, and the punbb forums go the width of the screen. I looked through the css and got dizzy, apparently many factors are styled together so when I change the width of one thing, it changes the width of several other things that I didn't want changed. I was wondering if there was an easy way to get the the whole forums page to fit in 600 pixels and centered. Any help is welcome, I'm in dire need of it!