I think this should be posted in the “Basics & Interface” section. Not sure what’s going on though… have you used Blender earlier on this computer? Does that happen in Blender 2.5?
I sometimes have a similar problem in 2.49 (not in 2.5 though). If I right-click and reset the Pane Alignment (to Horizontal, e.g.) it fixes it, at least for a while… I’m also on a Mac, so the odds are slim that this will help you; throwing it out anyway, just in case.
Seems to be a opengl graphics driver problem to me. I noticed similar display issues on machines with intel video chips that had older drivers installed, as well as crashes (opening and closing the preferences window in 2.5 would crash certain machines).
Make sure to install the newest geforce drivers, and test again. If the problems persist, try changing some of the opengl settings in your driver configuration panel. It’s a bit trial and error, though. You might even want to install more optimized community drivers from Guru3d and use Rivatuner as well to fix the problem. And delete the old remnants of drivers with driver sweep.