Hi wheat3000,
See this previous
post for information on how to update the BIOS.
You don't need a BIOS update to install XP SP2 and it probably wont fix your BSOD's either.
However, many years ago, I built a machine with the P4C800 mobo (with XP SP2) and it's now showing its age. It could be your motherboard or your hardware that's causing the Blue Screens.