Basically you need a card with decent pixel shaders. The following should work:
Radeon 8500 series? (8000 series definitely won't work)
Radeon 9500 series (9000 series won't work)
Radeon X series
GeForce FX5200 or higher (GF4 or lower won't work)
GeForce 6000 series ('LE' cards might not work)
GeForce 7000 series
If you can run Battlefield 2 you should be able to run this. Doesn't need much CPU grunt but you'll need a card with proper shaders :)
As for why the GF4 doesn't work, the reason is that pre-FX nVidia cards have only 96 registers available (as do the 8000 and 9000 series) and so can't run more complex shader programs while the 8500/9500 series have 256 registers and can. NVidia scrimped on the shaders in the GF4.
Radeon 8500 series? (8000 series definitely won't work)
Radeon 9500 series (9000 series won't work)
Radeon X series
GeForce FX5200 or higher (GF4 or lower won't work)
GeForce 6000 series ('LE' cards might not work)
GeForce 7000 series
If you can run Battlefield 2 you should be able to run this. Doesn't need much CPU grunt but you'll need a card with proper shaders :)
As for why the GF4 doesn't work, the reason is that pre-FX nVidia cards have only 96 registers available (as do the 8000 and 9000 series) and so can't run more complex shader programs while the 8500/9500 series have 256 registers and can. NVidia scrimped on the shaders in the GF4.