PS2 is the only true 128 bit console, actually, the Emotion Engine is 3 processors all working at 128 bits, and at 294 mhz, working in tandom on the same or seperate things, the EE is very very powerful
XBox CPU is 32 bits
GameCube CPU is 64 bits
Dreamcast CPU is 64 bits
but thats only the XBox CPU, its the GPU that is the star of the show in the XBox console, and that is definately 128 bits