sounding to me like ya need to update mobo drivers.
do you have built on sound?
sound causes simailar crashes.
make sure that in your bios setup that your agp is set to 2X,4X
or just reset to defaults.
also make sure your nvidia card is on irq 11.
pull the card out then pop in old card check for crashes.
while the old card is in remove old drivers shut down then install new card.
update mobo drivers.
also look for the name of motherboard it will be on the board it self that or just numbers copy them run a search in google.