You'll almost certainly need to reactivate Windows after bringing it into the VM--it's going to see truly massive hardware changes as *EVERYTHING* will have been replaced.

I wouldn't run a VM from an external drive--it's going to be *SLOW*. Note, also, that the disk images for VM's are just as big as the disks they replace although they can be demand-allocated (this causes a performance penalty).

I've never tried to do anything other than use an image built within the VM so I can't comment on how an import goes.