I've connected to an XP box on my home network just fine. The screen adjusted itself to 800x600. Be aware there is no keyboard input supported yet, you'll have to load up XP's accessibility keyboard and use that on the remote machine itself. Much faster than VNC however.
Be sure to restart your 770. Make sure that you have already established your connection before launching the application. It's very nice and very tiny. I found myself wishing microsoft would have a "remote tablet" feature (ha) or maybe just a more pocketpc-ish on-screen keyboard. For checking e-mail and things, it's quite handy.
