I'm using the same card as yours but I only experience a slight amount of lag. I'm using a modified nVidia driver from
OmegaDrivers.net.
1024x768 at max settings = playable (with decent amount of lag)
Specs:
AthlonXP 1500+ Palomino @ 1333 MHz, 266 MHz bus speed
2x256 MB DDR, generic, 266 MHz FSB
Inno3D nVidia GeForce FX5500 256MB 128Bit
200 GB Seagate PATA 7200 RPM