Since the upgrade to the newest version of vBulletin, there's a gap on either side of the screen, depending on your resolution. At 1280 x 1024, there's a few inches of gap on both sides of my screen. If I'm at 1024 x 768 on my laptop, the gap is gone.
If its just the text on a window then hold down ctrl and flick the roller on your mouse or if your mouse does not have a roller then hold Ctrl and press =