ATI Rage 128 would be adequate to the CPU. Older Radeons should work too (7000-8500, 9100, 9500, 9700).
I've had Celeron 333, 64MB RAM and 32MB Rage128 in Asus P2B and it was great for games back then. Then I upgraded memory (to 192MB), then CPU (to Celeron 600, overclocked to 900), then memory again...now it's Celeron 1.1GHz (modified and overclocked to 1364), 512MB RAM and 64MB Radeon 9100, still with the P2B
