Still there are people who are sticking on to windows 98/ME and some people dont even know about win VISTA or 7. It may take even a year for people to get convenient with windows 7.
Till now there is no windows OS released with x64 alone. We have both 32bit and 64bit in all the windows versions so far. This being the case how can there be a 128bit OS without the co-existence of 64bit or 32bit OS ??.