Try the following (this is for a Netgear DG834G) so you will have to tweek for your router:-
Log on to your router as admin.
Go to Services and set up a new service (Add Custom Service button):-
Name: Dawnspire
Type: TCP/UDP
Start Port: 3170 (or the number you chose when setting up your server)
Finish Port: 3170 (or the number you chose when setting up your server)
Click apply
Go to Firewall Rules and add an outbound service:-
Service: Dawnspire – the one you just set up)
Action: ALLOW Always
LAN User: Any
WAN User: Any
Click Apply
Now add an inbound service:-
Service: Dawnspire – the one you just set up)
Action: ALLOW Always
Send to LAN Server: enter the IP address of your PC (not the router IP address)
WAN User: Any
Click Apply
Hope the above helps - allowed me to get around my connection problems anyway

Just need someone to register the server for me now - hint hint