Mythbackend is the computer you're using to record your shows - i.e. your "Myth" PC. You will have assigned the IP to the PC - or it could be getting an IP via DHCP, in which case, I'd recommend setting a static IP for it to make setting up frontends easier. That way, it will always be at the same address.

To find an IP address, open an Xterm on the PC, and type "ipconfig" at the command prompt. You may need to be root to do this, or use sudo. Most likely, it's your eth0 IP address.

The port is the standard Myth port - don't recall it off the top of my head, but it's shown under the "General" setup section in myth.

As for getting it to work, I've had limited success. It is beta, but does work, sometimes. If you close it, and re-open it, it won't run, you have to reboot each time. In my case, it takes almost 15 minutes to find all the recorded shows after I start it.

I did not have to put the gms stuff on my backend, if you go the main maemo-myth webpage, there's a note that says if you transcode to a small resoultion, using mpeg-4, you can watch the programs directly. I do this for most programs anyway, so it streams OK, but pauses while watching a program aren't at all uncommon.

So..... long story short, it mostly works, and is a REALLY cool program, but it's not quite ready for primetime yet.