According to Mel Seder:
You may have to do a reset on the router box, then, to restore factory defaults, which means you'd have to reconfigure all the settings you had changed previously.
You'd only need to configure these if you want to allow FTP and SSH connections _in_ to a system behind the router. SSH is easy: it's tcp port 22.
FTP uses tcp port 21 for the control connection, and port 20 for the data connections, assuming you're using active-mode FTP. Since many FTP clients now use passive-mode FTP by default (to make it easier to work when going _out_ through a NAT-based router), you might have to enable an additional range of ports to allow for passive connections. Depending on which FTP server you set up, there may be a way to limit it to a particular range of ports for passive connections, which should (of course) match the settings on the router.
Bittorrent
According to the URL I provided earlier...
http://torrent.dulug.duke.edu/
"Open up ports 6881-6999/tcp so other clients can contact you for bits"
I would assume this is the only port range you need to open up on the router to fix the bittorrent problem.
If you know of a well done sight that lists other common ports would you please send me the URL.
Well, I usually consult /etc/services first, but not all of the ports you might want to know about will be listed, and those that are there may not be very well understood, since there's no description or reference info.
Here are URL's to some sites I've come across, which may be of use...
TCP/IP Common Ports (from MyServer.org Dynamic DNS Services) http://www.myserver.org/help/ports.asp
TCP/IP Ports for Internet Services http://www.chebucto.ns.ca/~rakerman/port-table.html
Ports for Internet Services http://www.eviescreations.com/ports.htm
Linnet Firewall TCP Ports http://www.linnetsol.co.uk/port-filter.asp
Internet Services by Port Number http://www.graphcomp.com/info/specs/ports.html
DoorStop Port List http://www.opendoor.com/doorstop/ports.html
TCP/IP Services http://bfs-test.acns.fsu.edu/Network/portDescription.shtml
Port Numbers for Port Forwarding http://kbserver.netgear.com/kb_web_files/n100495.asp
No single list I've found is exhaustive, but by looking at a few, you're likely to find a decent description of whatever port numbers you're looking for.