My laptop is too slow to play Doom 3 as it only has a single 2.1 ghz cpu and 1 gig of ram. Shame that.
Depends on cpu and gfx card specs, the internal frequency alone says not much.
I have played through Doom 3 on a a pc with 2.4 ghz pentium 4 (single core) cpu, nvidia gf 4200-ti gfx card with 64 mb video ram, and 512 mb of main ram. It isn't a lovely experience of course. But I have also played it on an AMD64 X2 5200+, ATI radeon x1700 SE 512 mb video ram, and 2 gb of main ram, and on such a system (already ancient for gaming) the game flows.