I've built mythTV 021, the current version in Synaptic, and also built mythTV 022 and passed on to contribs december last year. I'm sure it's due to the new iso's that this somewhat complicated package has not been included yet.
In the meantime, as the new iso's are built - I stepped up to mythTV 023, that is way better translated and feels smoother than 022.
The mythTV 023 is sent to contribs - and has been removed from the queue, so I expect you will find mythTV 023 anytime soon.
To answer your question, you need a rather large list of dependencies installed to be able to compile the base package and the plugins - if you are interested in the rpm building SPEC file, I'll gladly insert it here for you to look at (either use it in a packaging environment to play with it, or to see how to compile mythTV),
If you like compiling programs, I'll recommend you to setup a building environment in VMWare - just take a look at the sticky posts in 'Packagers' section - then you can help out updating and building packages from 'Package suggest' section,