Card wont do it alone. Im not sure what specs a stock system would need to run it at very high but id take a guess at:
4870 GDDR4 (the important bit), or X2. 9800s are **** house.
2-4GB RAM
Dual Core (or High Clocked Quad) - Pref Intel as they own atm.
Decent Motherboard.
Should do it. My system was miss matched bits n pieces and Crysis didnt really push it too much. There are games out now that are just as good
With a story line to boot!
If you want a game that will tax even the beefiest of rigs (i could barely get 20 fps) try CM9 for HL2