Just use one of the dozens of open-source VNC clients+servers: tightvnc, tiger, vino, x11vnc. x11vnc server was ported for Maemo4 so probably available for Maemo5 and there is a good vncviewer client as well. Yeah it's not the same and auth isn't compatible but still. Also you can combine hamachi/logmein or even ntop's n2n p2p VPN + one of the VNC servers + clients I mentioned.