Pages "waving" when scrolling

Hi!

I have a problem when scrolling. Pages don't roll smoothly but are kind of updated in a wave that goes across the screen.

It's a bit difficult to explain but the page isn't actually scrolling, it remains still while an updated screenshot of a slightly scrolled down version of the page rolls down in a wave from the top of the screen to the bottom.

I have Windows Xp amd I'm using Firefox 3 now but had the same problem in Explorer. And when I go to the options menu and enable soft scrolling it becomes worse and pages scroll/update very very very slowly. However, this is not limited to web browsing only but can be seen when looking around my own harddrive as well.

Any ideas what might be causing it?

 EDIT: Actually, it's not only when scrolling but when dragging windows on the screen as well. The window kind of makes a series of small jumps rather than smoothly floating across the screen as is the norm.