'Blocks' remain on screen

[Tony1701]

Client PC:
P3/1Ghz w/int. Intel CA810 Graphic Chipset
Running WXP Pro, Office XP, Norton AV.
Patched with all updates from Windows Update
Video driver latest from Intel
BIOS latest from Intel.

The problem is when the client minimizes a window (be it
Word, Excel, whatever), about 20% of the time a remnant is
left behind. This remnant is a rectangle shape, and can
be anywhere from 1 by 4", to 2 by 8". The remnant will
have the residual video of what was in that location
before the windows was minimized. It is not application
specific.

Maximizing the window does not get rid of that block. The
only way to remove it is to reboot.

We have:
-replaced the motherboard
-installed a video card in a PCI slot and ran off that
-rebuilt the OS
-all the updates listed above.

Any information on this problem would be appreciated.

Thanks,

Tony