the point of a VPN is to create a secure tunnel using pptp, ipsec or whatever. The VPN provides the tunnel, and you run your apps through the tunnel.
if you were thinking about using VNC, but want it secure, you can tunnel VNC through SSH which will give you a good amount of security. look it up on google on how to do this. I did this a while back and found some good articles on how to use putty (ssh client) to set up an ssh tunnel for VNC. I dont know if all VNCs will work happily in this setup so try using tightVNC or ultraVNC.