What sort of system will be required to play Doom 3?
Early indications suggest that the target system for Doom 3 will be a 700 mhz system with 128 megabytes of RAM and a "high-end" video card (assumably GeForce-level or higher). However, these specs are very tentative and will probably change multiple times. There will probably be versions released for Windows, Linux, and Mac.
In an interview on 9/18/00, John Carmack had the following to say about the Doom 3 engine and how fast it will run:
I am spending a huge amount of graphics horsepower to allow the engine to be flexible in ways that game engines have never been before. It is a little scary to drop down from the ultra-high frame rates we are used to with Q3, but I firmly believe that the power of the new engine will enable a whole new level of game content.
I am hoping that the absolute top-of-the-line system available when the game ships will be capable of running it with all features enabled and anti-aliasing on at 60hz, but even the fastest cards of today are going to have to run at fairly low resolutions to get decent frame rates. Many will choose to drop a feature or two to get some speed back, but they still won't be able to get near 60hz.
Remember, the game won't ship for a long time yet, and today's cards will seem a bit quaint by then.