I’ve built my own DVR using the excellent Linux-based MythTV software. I’ve written a detailed guide about how I did it here.
I mostly wrote it for my own benefit, but hopefully it will be of use to others too. If you’re into this kind of thing, please do take a look and let me know what you think in the comments secion.
This was a very fun project for me and in the end it turned out better than I expected, if anything. There is also plenty of potential for future expansion. My next step is probably getting a proper router so I can control the system via the remote web-based interface.