If your Going to Set up the VPN you may Need Full Access to your Router, it most likely has a built in Fire wall, that you'll have to configure in order for it to allow a VPN
Some Router's Let you Set a VPN up on them. This is some times the Easiest way.
If not there are two options ,
One you can Forward the Ports the VPN will use to a Server set up to Receive a Connection
Two you Can forward the IP to the Server, (witch may case problems if your network is at all advanced) but this will make setting up the VPN very easy but expose your server to the Internet , Well expose it more....
Now we need Details on the router , there are 3 ways of Getting in to routers , 1 a nice little Web interface, 2 a nice Easy Telnet interface, and 3 a serial console port using a telnet interface