Interesting question - see MS site
here, for example.
There used to be a Power Users group in XP.
The Power Users group in Windows XP was designed to enable members of the group to perform system tasks, such as installing applications without granting full administrator permissions.
Power Users also had write access to areas of the file system and registry that normally only allow administrator access. Power Users enabled some level of application compatibility; unfortunately, this did not address a fundamental problem: applications requiring unnecessary privileges and user rights.
UAC in Vista does not leverage the Power Users group, and the permissions granted to the Power Users group on Windows XP have been removed from Windows Vista. UAC enables standard users to perform all common configuration tasks.
The Power Users group, however, is still available for backwards compatibility with other versions of Windows.
To use the Power Users group on Windows Vista, a new security template must be applied to change the default permissions on system folders and the registry to grant Power Users group permissions equivalent to Windows XP.
Unfortunately, MS in their infinite wisdom have not actually said what or where this template might be.
Possibly secpol.msc. I don't have any copies of Vista that I can experiment with - google is probably your only friend.
SD