Well help is at hand! We've just released a new Knowledge Base article describing how to get the Admin Pack working on Windows Vista, and describing some of the limitations that will still exist.
Note that this does not address managing Windows Server "Longhorn" from a client machine (either Windows XP or Windows Vista). We are working on a new version of the Admin Pack for Windows Server "Longhorn" and we will provide an update on our progress with this in the Beta 3 timeframe. I assume this Longorn admin pack will support management of Win2k3 and maybe even win2k servers.