That's a screen capture from my desktop background in Vista. No matter what image I select as my background image, there's a weird box with a drop shadow showing up. It does not show up on other accounts on the box. It does not show up on windows (i.e., it's not a hardware problem so far as I can tell), just the desktop background.
Here you can see it with a solid color.
It's annoying. How to I get rid of it without scrapping my account and starting a fresh one?