My thoughts are you'd be better off port forwarding. AFAIK about BT Voyagers, they are better of port forwarded. If you are willing to take the plunge, then see Port Forwarding for the BT Voyager 2091 (same instructions as yours) with the most important step being the first, which is setting up a static ip.

Edit: OH ... ok ... if it's ok now then fine!

But if you're running XP with SP2 you might want to use one of these patches: MS & 3rd party patches