I have found a bug regarding the UI for Blender 2.56 for Windows (the one provided in the downloads section).
After certain actions (the most consistent for me being opening the user preferences window) the UI stops redrawing properly. I can still do things, but text usually doesn't draw and the panel backgrounds seem to not be cleared, causing the UI elements to simply be drawn over the old ones.
I can fix it by clicking around on buttons I can see until it works properly, but that "fix" only works 2-3 times before it no longer works. After that the only fix is to relaunch.
Most likely, this is an issue with your video card/driver. If you have updated your video driver and turned off any compositing window managers, you might try playing with the Window Draw Method on the System tab in User Prefs.
Not odd at all considering Blender using OpenGL for all its drawing. Your other programs, games for example, are likely using DirectX or other native Microsoft drawing libraries. If your video card/driver/settings do not do OpenGL well, you will have display issues.