Changes to COM in Windows Vista
The following changes appear in COM in Windows Vista:
The COM elevation moniker allows applications that are running under a limited user account (LUA) to activate COM classes with elevated functionality. For more information, please see The COM Elevation Moniker.
When you install an application that makes COM calls on a Windows Vista computer, and you plan to run the application as an administrator, you must install the application per-machine, rather than per-user, or it will not function properly.
[Note : Content is from MSDN]