Blender uses OpenGL, an accelerated 3D programming library, for its entire interface. Because of the extensive use of OpenGL, Blender often uses parts of the library that other programs may never touch. Depending what video card you have in your computer, the drivers for that card may not effectively implement these little-used library features that Blender needs.
On some machines, Blender may run very slow, or you may see weird screen glitches around the mouse pointer or menus. The first thing to check is the drivers for your video card. Go to the Web site for the manufacturer of your video card to see whether any updates are available.
You may want to turn off any fancy effects that your operating system adds, such as transparent windows, shadows on the mouse cursor, or 3D desktop effects. Because all these little bits of eye candy tend to be hardware accelerated, they may be conflicting with Blender a bit. At the very least, turning them off usually makes your computer use fewer resources like processor power and memory, thereby making more of those resources available to Blender. If you're using an nVidia video card, make sure that the Flipping check box in your OpenGL settings isn't enabled and that full-screen anti-aliasing is disabled.
Within Blender itself, go to the System section in User Preferences (Ctrl+Alt+U) and find the Window ...