Couple things...
When using VNC - try Chicken of the VNC, seems to be a little easier to configure. Try connecting in the form of your IP address to the outside world and don't forget the port # of the viewer (usually 5900) Make sure that you you have a password enabled on the server as that is usually why it disconnects.
I am by no means an expert on this, you can search osxhints.com for some answers as well, like I did at first.
Don't give up, once you understand how to connect the possibilites are endless!
I use VNC on my pocketPC to look at my home computer and to run my powerbook ala Salling Clicker.
Cheers!