Strange Video Driver Pixelation Problem

[Kristopher Kerwin]

I seem to be having a strange pixelation problem. Rather than try to explain 
it, I've included the following pictures that show the progression of the 
issue:

http://img524.imageshack.us/img524/221/xorgproblem1aq7.jpg
http://img99.imageshack.us/img99/4314/xorgproblem2vv0.jpg
http://img222.imageshack.us/img222/9727/xorgproblem3bt9.jpg

The problem doesn't manifest itself until a while after the machine has been 
running. Movement of windows across the screen seems to make the problem 
worse, as does scrolling windows. 

Highlighting text in a window, or dragging another window over an affected one 
seems to get rid of the pixelation. (Notice the bottom right corner of the 
window shown in the third picture: the pixelation stops there where another 
window was dragged over that point.)

The problem also occurs in the CLI, but does not seem to occur when I dual 
boot to Windows, suggesting that it is not a hardware issue, but rather a 
driver issue. Also, the fact that I can capture the problem in a screenshot 
also suggests that this is not a hardware issue.

What sorts of diagnostics, if any, can I give that would help figure out the 
problem?

Thanks in advance,
Kris Kerwin