Gamespy claims to have the scoop on the specifications of the next generation Xbox (codename Xenon). As previously suspected (see block diagram below), the CPU is a triple-core highly clocked PowerPC part, although the speed has now dropped from 3.5 GHz to 3.0 GHz.
Click on picture for complete diagram.
Each core is described as being capable of issuing two instructions per clock, and from the diagram we know that it has a vector unit (which likely supports VMX/Altivec). Thus, it seems that Xenon's CPU cores are very similar to the PPE unit in Cell.
Also of interest is Gamespy's claim that current developer kits have machines with two cores instead of three. In my previous Cell article, I stated that if Apple were to use a chip related to Cell, it would lose the XDR controller and likely all the SPE units as well. A highly clocked dual-core PPE-based chip would be the most appropriate, and this is very similar to what Gamespy is describing for the current developer kits. (That is assuming of course that the developer kits are not in fact still dual single-core machines like the dual G5 Power Macs, which were rumoured to be in the initial developer kits.)
However, I still believe that Apple's next chip will be an extension of the G5 series, either the dual-core 970MP or the single-core 970GX or both.