256MB 6800GT, but I think it's the combination of old CPU (Athlon XP2600+) and slow unbranded DDR RAM (despite it being 2GB) that slows it down, not the graphics card...

Desktop runs perfectly at 1600x1200 @ 85Hz, not sure what frequency the game runs at.

New spec should see it running a bit more smoothly (I like understatements ):

Athlon64-4000
2GB cas2-3-2-5 PC3200 DDR2 OCZ Platinum RAM
2 * 512MB XFX GeForce 7800GTX XXX-Edition (I really will have no money left after buying these )