Yes, if all goes to plan (since Merom supports virtualisation) as does Leopard (which will support virtualisation) you will be able to switch between Mac OSX and Windows XP (and eventually, Vista) just as you could switch between users on Mac OSX. Notice how Merom and Leopard are due out at nearly the exact same time? [August-November] There was a reason for it ...
Funny how that works? Apple is like Intel's new "toy" :-\