Just use Ubuntu and if possible, install the Mythbuntu package. I think I've seen the option, but haven't specifically gone looking for Mythbuntu though.
It just seems like I will have a whole lot of extra stuff when I basically want a dedicated mythtv box, at least I think that's what I want. Will probably end up adding other stuff to it, but basically just need a basic old system hooked up to the TV so I can watch stuff there, don't even have a DVD player on my TV.
i followed the above the first time i installed mythtv on debian. the problem is that lenny has now replaced etch. so you would at the least need to replace any references to etch with lenny or stable (i would choose stable).
what i would suggest is to learn enough about linux to install your own system. and then install the necessary packages. having far greater control over your system gives you the opportunity to make far better decisions regarding upgrades. i say this from first installing mythtv from a bog standard install.