There are many variants of VNC, which one you are referring to? RealVNC, TightVNC, UltraVNC, etc.?
Also, AFAIK in order to use VNC, the system you connect to should have either a public IP or some sort of port-forwarding/NAT punching, etc.
My ISP puts me behind a NAT of some sort, so i can't make a connection from outside to my home PC.
I am looking for a solution which has a central server to help facilitate a connection, just the way Teamviewer does.