Doom 3 hardware guide available
 

Hardocp has released their Doom 3 hardware guide. If you plan on playing it when it comes out then this is a must read. Hardocp basically gets a bunch of PCs with different hardware configurations and video cards. Runs Doom 3 on them and configures the video settings for optimal performance. For example, if you have a P4 2.8 and a Radeon 9700 you should run at Medium quality with noAA and 4x AF. Stuff like that.