... and 686B strikes again. somehow, I'm not surprised.
Find the latest 4-in-1 "patch" which is recommended for KT133A, not sure which it is. There've been so many damn releases and patches I'm dizzy.
You might also try adjusting PCI latency, either through the BIOS or with WPCREDIT. It's a tedious process I don't recommend unless you really have no other choice.
You could also try different PCI slots.