You'll probably get completely different answers from different people but here's what I had to do.
My ISP uses the IP for the machine, not for the modem, so make sure of which one your ISP uses. Anyway I had to enter in the MAC address for my machine itself into the appropriate setup page for the router. It still wouldn't work even with the correct ports opened. Finally the only way I could get it to work was to put the router on DMZ. Then I had to wait for the countdown when logging into the Access Server to ask me to manually enter my IP address. Now it works great.
Just make sure you have a good software firewall if you are using DMZ since your router won't block ANYTHING after that.
Good luck
Sir William