Heaven forbid that I should disagree with David and Dr. F but ... actually "disagree" is not the right word - "explain to a fellow know-little like myself" would be more appropriate.
I seem to recall that the primary difference when configuring a VPN connection is that I need to use the system name, IP, whatever that I would use _inside_ the local network. Not necessarily the same as the one I would normally use to connect from outside. In my case to connect from outside I use systemideveleloper.com - within the confines of the VPN I simply use ideveloper as if I were on the local LAN. That almost certainly an over simplification but it is the way that I remember it.