MyBB Question.

[iRun]

Okay first go to my forum, www.ideviceforums.net . Notice how it doesn't really expand much. It's basically just centered in the screen. Okay now look at SF. Notice how when you shrink the size of the screen, the site fill up the screen. How would I do that with my forum?

[DAMINK™]

Your forum is using a fixed width in the theme where SF is using a Fluid style.
Either change this in the theme settings or get a new theme that is Fluid i guess.

[Peter L]

Increase the percentage in your global.css

[DAMINK™]

Increasing the Percentage will not give the result he wants.
He wants a fluid site like this where it always fits the window.

[iRun]

Your forum is using a fixed width in the theme where SF is using a Fluid style.
Either change this in the theme settings or get a new theme that is Fluid i guess.

Where could I change this is in the settings? Like the templates?

[AceInfinity]

Templates don't have CSS, you need to edit the CSS, and maybe even a couple images if the new setting doesn't agree with the size or witdh of some of the current images. If it is a good theme, you shouldn't have any trouble expanding it, since lots of good webmasters interpret that, and plan for that scenario.