Hi, yes you do need to allow these ports in the firewall.
I think that this is to open the firewall to allow other machines participating in the bittorrent download to send me parts of the iso file and get parts from me that I have already received. Is that right?
yes.
I looked at Yast Firewall Configuration: Services/Edit additional services, and found that I could open ports 6881:6889 for tcp, but I don't see how to limit the uses of these ports to bittorrent. Does this have to be done?
This is the way to do it, but there is no way to limit the port usage to a program.
If not, what is the best way to do a temporary iptables change to enable bittorrent without letting anything else into my computer? Should I use a script file to enable/disable bittorrent?
Why not just allow the ports? BitTorrent will be the only application using it. Allowing 6881:6889 through the firewall doesn't mean your computer is vulnerable. Just don't run another on that port. Andreas