You might just consider MySetTopBox in conjunction with KnoppMyth the ISO install for MythTV. Could make it easy beans, maybe. I've not done it, but have a friend who is also on the cusp of trying this too. Also they have a forum of users and a KnoppMyth Wiki site for those who are in need.

Overall, It seems to be a pretty good solution if you can get the hardware in the right pile...