VPN Connection

Hi,
I have a two PC, one connected to the internet with a modem(Classic Dial Up connection) and the other with a router (ADSL) I made a VPN connection between those two PC
The ADSL one connect with IP adress of the Dial up one
Now i want to make it Vice Versa
The Dial Up one connect to the ADSL one
The problem “is there an advanced setting ?” and how to know the IP adress of ADSL Connection
Omar Abid