I would be inclined to believe Toshiba on this although I would suggest MS are looking at the Toshiba HD DVD slim drive to fit into any future 360HD model.
After all once you have a HD DVD Slim them you have very little additional componetry that cannot be slotted into the existing 360.
5
After all once you have a HD DVD Slim them you have very little additional componetry that cannot be slotted into the existing 360.