VNC doesn't work with linux the way it works with windows. In linux it doesn't seem to do desktop sharing (at least not that I've been able to find. I'm sure someone will correct me if I'm wrong).
If you want to share a desktop and your freind is running KDE, you'll want to check out KDE Destop Sharing
. I've never used it, but it sounds more like it will do what you want.
By the way, you should probably check into running this over an SSH tunnel so you aren't doing things like sending usernames and passwords across the internet in plain text. VNC has no encryption capabilities and I doubt KDE Desktop Sharing does either.