Doom 3 Minimum Specs Revealed
Thanks to The Phobos Lab, a Doom fansite, for their info, directly from John Carmack, that the minimum specs for Doom 3 will be "1GHz CPU, 256MB RAM, GF1 or Radeon 7xxx series card." There's no word yet on recommended specs to get the best fidelity, but sites such as NewDoom.com and The Phobos Lab are keeping a close eye on the situation, including an interesting but very unconfirmed rumor that "a Doom 3 demo [will be available] for public playing at this year's QuakeCon" - probably wishful thinking, although Carmack is scheduled to speak there, and it's possible at least some new Doom details will be revealed.
There 's a nice article on Tom's hardware.
You need at least a R9600/FX5600 to play at a descent frame rate.
It will be coming out for all three (Win, OS X, Linux) platforms. Carmack's use of OpenGL makes the port pretty easy. Also, I personally think there's a bit of a chance of some more Linux ports now that Mac uses unixy coding systems (note how fast America's Army came out for the Mac after the Linux version. It's because of how much code was sharable between the two.) Of course, as Id always does, it'll make us pay a bundle to upgrade our computers cause we like the pretty things.
Selling games is a part of, but not all of, id's income. id gets a significant amount of revenue from licensing their game engines. Consequently, it's perfectly acceptable for them to release a game with extremely high system requirements. Games produced by 3rd party developers will come out much later than id's engine "demo" game (e.g. Doom 3, Quake 3, etc...), giving system specs time to catch up.