Netgear Prosafe FVS318N Router - Configuring VPN?

After scouring the internet for weeks I've hit a road block trying to figure this out. I've got a Netgear Prosafe FVS318N router that I am trying to enable VPN on for my office. I've read all sorts of information online about port forwarding, VPN policies, and many other things that ultimately don't tell me how to set up VPN on my specific router.Now, I've set up PPTPD on an in-house linuxbox as a makeshift VPN server and I'm successfully able to establish a VPN connection to it from a local connection (e.g. 192.168.etc. local ip address). However, when I try and VPN connect from a client outside of my office's network, I try connecting to my router's external ip address and this yields no success. My ASSUMPTION is that this has to do with a port not being properly forwarded, or something of that nature.What are the necessary steps I can take with my specific router and router firmware, which is 4.0.1-66, in order to get a VPN server up and running that listens to outside connections?