I've just installed this software on my Linux PC at home, and it enables me to control the PC from anywhere in the world, same as VNC. However, it runs over SSH (port 22) which is secure.
I've got the client working at work, so I'm browsing the web at work on my PC at home, and all they will see is a connection from my PC on port 22.
It's very fast as well. My connection at home is currently about 5.5mb, and using it from work is like being sat at my PC at home. I'm also downloading from an FTP server as well at 150kbps, and that has made no difference at all.
http://www.nomachine.com/
I'm well impressed, they also do the server for windows as well, so I'm going to try it on that next week.