I've been studying this issue for several hours and it seem I still don't have enough information. Would you please do the following:
Post the entire message.
Run the MS memory diagnostic tool from http://oca.microsoft.com/en/windiag.asp
(Run the extended test by pressing T while Windows Memory Diagnostic is running.
Let it run overnight, and post results -- any failures?)
If the RAM checks out ok, I suspect a driver is trying to free memory that is already free. The most likely thing would be your video driver, though it could be any. Did you install XP with a Original Equipment Manufacturer's CD/DVD or a retail version?
Sorry this is turning into a long process.