Now software has advanced significantly, and I may consider a mythTV box instead of what I was going to do (custom software, because nothing out there does exactly what I want)

I know what you mean. It looks like MythTV may finally have enough neatness for it to be worthwhile - the built-in DiVX player is neat for me, and support for the Hauppage PVR-350 hardware mpeg2 encoder is sweet.