I've finally put together a DVR out of spare parts. I built one before (and even got mentioned in Wired magazine), making my regular desktop do double duty, with a wireless 802.11B connection to the living room. On the TV side, a small Linux box (Hauppauge MediaMVP) decoded the video and handled the remote. It worked well about 95% of the time, but when it didn't work, it was a nightmare to troubleshoot. And you couldn't use the microwave, talk on the phone, or look funny at it... It also took me a month to build - mostly spent researching and tuning my network connection and figuring out my way around FFMPEG to compress the video.
When we moved to another house, it just wouldn't work reliably anymore, no matter what I did. I ditched the project for awhile, but picked it back up again when I got a free 10-year old computer - a Celeron 733Mhz with 64MB RAM. This was more an exercise in getting a slimmed down version of Linux (Mythbuntu/Xubuntu) to work more than anything else. I was able to get it to record shows, but not play them :-)
A few weeks ago, my neighbor gave me an old Dell 4300 1.8GHz machine. It wouldn't boot, but I found out that all it needed was a new power supply. I put an nVidia 5200 128MB card in it, a new quieter fan, and 1GB of RAM that I had saved from another dead computer, and it runs XP Media Center 2005 great (as long as you buy the $20 nVidia PureVideo software - not sure why this is required, but it is). It even runs Hulu perfectly (if you set it to medium quality) via a browser, but it chokes using Hulu desktop for some reason.
So now my kids are happy b/c they always have their PBS shows on tap, and my wife is happy, as she can watch her CBS shows. And this one only took me a few hours to set up. The thorn has been removed from my side.