The Gforce 6600 is the lowest nvidia based card with shader 3.0 that I could find....
It ran great on my ancient Athalon XP-2700+ , Gforce 6800GT, IGig of ram and a CRT at 1024x768 with medium settings
Everyone in the room oooh & ahhh'ed throught out the demo
"Don't like my driving?
Then quit watching me"