I just installed Vista, and I can't update my graphics card drivers or I will get this problem at the welcome screen. This same glitch used to happen on XP with certain games. It happened very frequently while playing Warcraft 3, and occasionally playing other games as well.
But on Vista, it happens all the time.
I am running on a GeForce 7900 GT/GTO
I used my camera to take a picture, because I think if I take a screenshot it shows what the desktop SHOULD look like.
Here it is (it changes color depending on the background btw):
I am doing all this in safe mode right now, because even with the default driver it installs it is still doing it.