I tried KnoppMyth (a bundled version of MythTv and Knoppix designed specifically for a PVR) once but had some issues with my tuner card. About a month ago, I installed Ubuntu Dapper Drake and installed MythTv through apt-get.
After a bit of tweaking, it worked perfect.
It isn't terribly difficult, but it can take some time. I suggest following an install guide for a specific flavor of linux.