While there is no major difference in the underlying security model in XP and Vista, there are many small changes that you should be aware of—the most important being the role of local groups and privileges assigned to them.
A privilege is the ability (or right) of a user account or group to perform a specified system task. For instance, changing the system time is considered a system task and therefore requires the
Change the system time privilege.
In Vista, Microsoft deprecated the role of the Power Users group, which had often been used by system administrators to grant additional privileges to users on their PCs, but was essentially the same as the Administrators group with a few less rights. ...