Yes, this is tricky. Vista is set up to allow the opposite - using one user
for most features and then run as / elevating to an administrator account
for some programs.
I think you should be able to get Run As Administrator to operate (pretty
much) the same way XP's Run As did by modifying group policy, but this would
also affect UAC dialogs, so it would force administrators to re-authenticate
every time they opened an administrative tool, which is probably not
something you desire.
I guess a "propper" solution will have to come from a third-party in the
form of a shell extension (or maybe power toy? would be a good idea for
Windows Vista Support Faq http://www.jimmah.com/vista/