I personally hope it has an AMD possibly 2-3 ghz. Hopefully it would be more because those chips would be laughable by 2005-06. AMD can give better gaming performance than Intel at a much cheaper price.
I'm not sure between ATI, Nvidia or Matrox. ATI can be the same as Nvidia (except some bad drivers) and it has special features that can't be seen on Nvidia. But Nvidia has better drivers and also has features that can't be on ATI. Matrox is like the underdog, X-Box. It's better than both (like PS2 and Gamecube, but I like my Gamecube more than my PS2), has loads of features not seen on any of the 2 and it's not given a whole lot of credit for its potential. Matrox supports 16x anti-aliasing while the others have 4x AA. It doesn't suffer while AA and Anisotropic are turned on because it'll have 256 DDR. Of course by 2005-06 chips will be using 512 or more. It will also use 10 bits per color (can you imagine that on an HDTV?). With this it can blend many textures together, imagine Halo/Halo 2 with ultra realistic textures (probably give someone a seizure).
For RAM I hope they use 256 or 521. That way there's no excuse not to make a game for X-Box. Since X-Box is a console it won't run other programs than a PC. So we will definately be seeing a lot more PC titles on the X-Box.
The Hard Drive could be 20-30 gb. Like I said by 2005-06 a lot of the stuff available today will be laughable because PC hardware constantly evolves.
So that's what I hope (doesn't mean it'll actually be that way), post what you hope the X-Box 2 will be like. Please none of that it converts into a super robot and destroys every other gaming system until it's the last one standing.