Yup, you can use client side Vista and have the remote server running Vista. If your client can do Aero, you'll get the full glass when doing RDP.
Not only that:
Since Longhorn Server support remote applications (instead of teh full desktop, you can "remote" into specific apps - like Citrix, forgot what they call it in LH server). Now when you use a Vista Client (with aero capable hardware), and open a remote application, your app will also get full glass support.
On the newsgroups they mentioned that the RDP 3.0 for downlevel OS is coming soon on the connect site. That would mean (I don't have a confirmation on this) that we can remote term in from a XP client box (to Vista remote machine) and alos do that app sharing thing from XP. (no glass though, coz XP doesn't have the concept of glass/aero)