PlanetQuake has some information about Quake IV from the QuakeCon2003 keynote speech from the Id software crew! here are a few quotes:
Q Is Quake IV next (after Doom3)?
A: There is a possibility that we may see Quake IV at next yeat's QuakeCon. Tim is currently directing the team at Raven.
Q: What will the minimum requirements be for Quake IV?
A: Too difficult to forecast this point. But to run it well you will likely need at least a GeForce 2, 256MB RAM and at least a 1GB processor.
Q: What key features will separate Quake IV from Quake 3?
A: Quake IV is a continuation of Quake 2, back on Stroggos fighting the Strogg in the single player. They are planning different types of gameplay such as vehicles and other elements.
Q: Will there be strafe jumping in Quake IV and Doom 3?
A: It's slower, but the physics are there.
The system requirements are still not too high, but at least a 1GB processor?! Most likely they will mean a 1GHz processor don't you think