Windows uses an interface called "
GDI" to draw objects. Modern graphics cards have a GDI accellerator, which does some of the window-drawing stuff that I guess would otherwise have to be done in software.
It seems that the generic graphics driver in Windows XP does a pretty crappy job of some forms of motion (most notably, scrolling windows or moving windows) with this accelleration turned on. I believe if you lower the graphics accelleration level (in the advanced section of the Display control panel), things work fine with the generic graphics driver.
Sidetracking...
Interestingly enough, Microsoft is moving the GDI functions back to software for Windows Vista (when the desktop composition engine, i.e. the pretty graphics, are enabled). Standard 2D windows will be drawn in software, however, the graphics card will be used to draw all of the windows, and the 2D windows will be stored as 3D objects (or something) in the graphics card memory. Since all windows will be stored all the time (as opposed to just the ones that are visible, as is what happens right now), this eliminates some Windows visual problems, like the visual "re-draw" you can see when dragging a window off of another window (particularly on slower machines), a delay while Windows re-draws a window while you are switching between full-screen apps (particularly visible when you are messing with some fancy stuff in an application like Photoshop), and a window that stops drawing stuff or turns white while an application is hung.
