From what I've read Umbran, I believe there are two models of Win8 tablet coming, the lower cost will compete directly with it's brethren as a purely mobile tablet device, runs on the ARM chipset, and you are locked into the "Metro" UI only. The more expensive version, (running around $1000, could be less or more costly), will be a full computer in tablet form, and can go to a traditional desktop UI, and can have programs installed in desktop fashion.. although it lacks a cd/dvd drive, so it'll require either software only installers most likely. At least that's what I've read on several gadget sites. Perhaps that info is out of date however..?
I've seen some waffling on the ARM=Metro only, but on the technical front, it looks like ARM will only run the Metro stack.
ARM is a wimpy processor and can only run stuff compiled for it. Desktop mode is running the full win7 x86-style stack and that software cannot run on ARM.
This did raise some interesting questions in my .NET community about whether the Metro marketplace for software had to carry both ARM and x86 versions of the app, and whether that would be seperate downloads.
You can't install a Metro app from outside the MS marketplace, per the last details I'd heard. Just like an iThing.