As we're fine tuning the performance now, it looks like the specs are going to be the same as last year. That being said, we have a rig with a 1.2ghz Celeron, 512MB ram, and an x800 that is running ~15-20 FPS on the lowest settings. That should give you an indication of how much better the performance is this year on lower end systems.
Shader Model 2.0 is fully supported this year, though the system requirements are going to say 3.0 or higher.
Rejoice and be glad peoples