Wintel Platform
If the Surface is a true Wintel platform, then it should be able to run Win7, and possibly Win XP 64-bit (drivers being an issue.) 7 And XP may not handle the touch screen too well, but (again with the drivers) could handle the pen input. An interesting thing to look at is to see if someone can get the touch screen input to translate to something like touch pad input, for times when it's inconvenient to use the actual pad on the keycover. As for the rest of the hardware, the specs look like about everything else that Win 7 already runs on with Ultrabooks. Don't forget there's always virtual XP mode over Win7/8--have fun with that.