for what I Know, at E3 time there was no ps3 hardware ready, the only cell based machine was a 'server' with two cell @ 2.4 Ghz, and this is the machine behing the demos
I think that 1 cell do rendering, the other manage the physics (this was the original ps3 project, before sony kick off the toshiba gpu to take in the nvidia gpu)
if you search, you can find some images of the dual cell machine (seems a big big metallic cube)