JDC2000 is correct – typically VPN connections are not made to work through the same router / network as they are intended to allow incoming connections to internal resources from outside a particular network. However, with that said, aside from configuring the Windows 7 VPN server machine to accept incoming connections and then configuring outgoing connections for the VPN connection on the Windows 7 client side you do need to enable port forwarding for on your router / firewall.

Presuming you chose to create a PPTP VPN connection, you will need to enable port forwarding for port 1723. For additional protocols / services and the ports that correspond to each, VPN and Remote Access Connections Fail is a great TechNet resource.

Jessica
Windows Outreach Team – IT Pro