With 1gb of ram, I can play (with a 6800, not loads better than that card) HL2 on high settings, 4XAA 8X AF with 1280 X 1024 resolution above 60FPS. On CS:S stress test I get 80-90FPS. With only 512, I get lag on medium settings.
So yes it will play DOOM 3 With good settings and frame rate, as long as you have 1gb of ram. If you can't afford it, get cheaper ram, as Corsair isn't good for overclocking, and is overpriced. If you are overclocking, OCZ platinum rev. 2 are great overclockers, and is I think £140 for 1gb.
is a good site as well.