TheRegister reports on a leaked report from a Chinese forum that claims to detail Xbox 2 specs.
The specs seem to include three-core 3.5GHz CPU. This is presumed to be a PowerPC/IBM design, though it is not specifically reported to be a PowerPC.
Several other sites are referencing the chip as a 976 PowerPC. As far as we can tell, all references of PowerPC 975/976 appear to be the product of unreliable/fabricated rumor reports. As a result, the 975/976 is not considered to be an actual product (...yet).