Not a whole lot has changed in the Virtual world when it comes to running Vista.  Virtual PC still can't read ISO images over 2.2GB, so you'll still need to mount the image on the host PC, or burn it to a disc and use pass through to get the disc inside the VM.

The only real change is... <drumroll /> ... the need for an updated set of the VM Additions.

To get the new Additions, head over to Connect, and get into the Virtual Server 2005 R2 SP1 beta.  Once you're in, you'll need to download Virtual Server, not the Beta 2 VM Additions.  Once you've installed Virtual Server, you can use the Additions ISO file it copies down to install in your Vista VM.  Now, keep in mind, you don't actually have to use the beta copy of Virtual Server 2005 R2 SP1 - that's just where the Additions are.