We've been discussing some of the changes in the Windows Vista security model.  Here is some information on another one.

In Windows 2000 or XP with ActiveSync 4.x, if you use a limited user account (non administrative), you cannot install the ITScriptNet Client to a device.  ActiveSync 4.x requires an administrative account for device installation.

In Vista, the UAC will pop up a username/password prompt, and if you supply the correct credentials, you can install the client to a device.

We've added a Knowledge Base article describing this issue.
INFO: ActiveSync 4.x requires an Administrative account to install