Vista - Virtual backup DC

I need to temporarily set up a Server2003 domain controller, to last until
acquisition of a new physical server. It will not have a heavy load, just
basically sitting there holding a backup copy of AD. Would Virtual PC or
Virtual Server be the better choice to host this VM on a Vista Business
32-bit host? As I understand, VS can run as a service without requiring
logging on, and all other things being equal that may be the deciding
factor, except that I already have VPC2007 installed on the Vista host, and
have never used VS.

Also, would it matter that the Vista host is already a member of the domain
that will be on the virtual DC?

Thanks for any advice,
Dave