yeah it's been going around the net past few days.
I'm highly doubtful. Windows 8 runs on X86, with the new addition of ARM. Xbox 360 is a PPC chip. It'd require a hefty bit of hardware emulation. Modern PC's are just getting the hang of the PS2.
It doesn't make much sense either. Most of the 360 library is old, and it'll be well in it's twilight years when Win 8 comes out. So a fair chunk is either multi-plat, so already on PC, or will be bought used. At this point people who've really wanted a 360 would have bought one. Wired pads are seemingly being phased out which would make playing 360 games a pain (yeah there's the receiver, but it's like £25. A bit of a hefty sum tbh)
It just seems such a pointless thing that I don't see it happening. I don't really see the money to be made in it, which is about the only reason MS would do this given people are already making games specifically for PC, without the need for emulation, anyway.