No chance since id are pro PC and I'm sure Microsoft will give some extra incentive for Doom III to be an exclusive. Personally I don't think the port of Doom III would struggle on the Xbox since its using a lower resolution (less video mem used) and it is using an nVidia card anyway. The only thing id would have to do is to convert the PC Doom III (which is Direct X9) into an optimised DX8 version. Hardly a hard task for the very talented programmers at id. Things like AA is a must so it'll be interesting to see if the framerate is locked at 60.