Do you have the mothboard driver disc ? just use that.
You'll see the model number on the board itself.
I bet it's GA- K8sumthn. find it and google it.
All you need to confirm is that it uses the nForce chipset
Most like sounds like nForce3 250
Find that out then go here.
http://www.nvidia.com/Download/index.aspx?lang=en-us
Choose nForce. 2000 Professional means nForce2, 3000= nForce3
Heck of alot easier then swapping the guts over.