Port 6346 is the default, but apparently any will do. I forwarded/mapped both 6347 and 6346 to the internal IP of my machine, and gave the other machines 6348 and so on. If you want the other machines to be able to access gnutella too, this means having to set each machine with a static internal IP and each client has to match the port assigned. Luckily the Linksys router I use came with toll-free support and et voilà also posted about the Linksys set-up. I went through all this a month or so back, but am still not confident here.
Posting your specs would help--especially of your router brand, platform, and versions.
The info about routers is usually vague because there are so many combinations. You probably saw that in the FAQ's. Search for posts by "Blackbird" to see how he posts his specs and for info on the 2Wire. I'm on OS 10.2.6 so don't have much experience with Windows Firewalls and router set-ups.
Hope those names help your searches.

Cheers