As far as I know, it isn't. Id decided from the beginning they were going to port it to the XBox and the Xbox alone, which is very strange... the Doom3 engine is written in OpenGL, which meant a massive effort to translate it into DirectX, and because of the pitiful power of the XBox (It's a flippin' Celeron 733Mhz and GeForce 3, for cryin' out loud!), quality of the game is greatly reduced (The screenshots, while still impressive, are nothing compared to how the PC version looks, and I guess that the framerate for the XBox version will be 15 at best). Personally, It would have been a far better idea for Id to port it to the Mac, then you'd have reason to have those dual G5 machines! (A Linux version would also have been nice, but if this emulator is for real, then I'll eventually be able to completely ditch Windows)
Wake up, George Lucas... The Matrix has you...