I recently replaced my NetComm NB5Plus4W recently and had a bit of trouble getting my NetGear DGN2000 modem router to forward the ports properly.
Unfortunately, it was hidden under an unexpected link. Luckily, it was quite easy to configure.
Log in to your DGN2000 router configuration page at http://192.168.0.1 and click on "Firewall Rules" on the left side column.
Under "Inbound Services", click "Add".
Select the port range you want (or to forward everything, select "Any(ALL)") from the service list and "ALLOW always" for action.
Enter in the IP address of the machine you want the information to be relayed to under "Send to LAN server" and select "Any" for "WAN Users".
Disable logging in case you don't want the log to be filled up.
Apply and finish up to add the new rule.
Now click apply to save the new settings for the firewall.
To test if the port forwarding has worked, use this page from uTorrent and it should give you a big green tick if port 58139 is forwarded correctly.
*edit 30/11/2009* - If you find your router is freezing up often, see Netgear DGN2000 overheating issues.