VPN and port forwarding

I'm wanting to setup VPN connections to multiple computers. We don't have an admin so I get to do all the networking since I can do a little more than turn a computer on. Windows VPN uses port 1723 only so I can put that into my routers routing table and get one vpn connection to one computer at it's IP address. How can I add another connection to the routing table so that someone else can connect to their computer on port 1723 while I'm connected to mine. For example.

My iphone @ ip xxx.xxx.xxx.xxx through external port 1723 to internal port 1723 to my desktop @ ip yyy.yyy.yyy.yyy

and...

Laptop @ ip xxx.xxx.xxx.xyy through external port ???? to internal port 1723 to their desktop @ ip yyy.yyy.yyy.yyx

Doest that make sense? Is it possible? I'm guessing that I will probably have to replace the router with a more high end device because this probably only allows 1 to 1 translation. We are using a Linksys WRT310N. Thanks

jeff