I'm currently using Multiplicity with Vista. I've also used KaVoom KM with Vista. Both work fine except Multiplicity seems more reliable for copy/paste across machines. HotkeyNet is what I use to send commands to my main and remotes. Both Multiplicity and KaVoom can use hotkeys to switch control back and forth. I use a HotkeyNet macro to switch control and center the mouse cursor at the same time. HotkeyNet is definitely worth a look!

Edit: Grr, I forgot to say that, at one time I was using Vista as the main and XP on a secondary. KaVoom KMhas a free trial period I think, BTW.