I work at a retailer that uses custom POS systems running on XP. These are low-end systems (512-1024 MB RAM). After the latest round of patches, many of these systems either ran out of system resources or would simply blue-screen and reboot. I originally attributed it to a patch + Intel video driver + Symantec, since I could disable either SEP, or the Intel video driver, and all would be fine. We originally had end users hit F8 and roll back to the Last Known Good, and that would fix it...until patches are applied again.
Interestingly enough, I've found that reducing the shared video memory in the systems' BIOS to 8 MB (from 32 MB) does the trick for these systems.
I can basically re-create the entire problem by re-installing XP SP3 + all patches, latest drivers, then install Symantec, and the problem starts.