if its AGP.. you probably have only 1 agp slot on mobo..
Do this..
Right click my computer desktop icon.
select proppties
click hardware tab
click Device Manager button
from the tree find your grapics card,
Right click the GC in the tree and select unistall..
SHUTDOWN your pc
remove old GC and replace with new..
Power up.. install new drivers.. (might be worth downlaoding any updates 1st)