judging from leaked benchies of the 6800GT and 9800XT doing a Doom 3 benchmark, i'd say you need at least a radeon 9600 to play doom 3 at above 800x600 and low detail. If you're absolutely gearing up for that game, best mobile video on the market right now is radeon 9700. And I'd suggest upgrading to 1GIG of ram. That should cut it. Don't expect to play it at 1024x768 and high detail tho.