If you're a really hardcore hacker (and I hope you are
) you should check out
Freevo and
MythTV. Both are Linux applications that turn any old* PC into a TiVo unit. They're totally free too. All you need is the video capture hardware, like one of those WinTV cards available from BestBuy and Buy.com for a little over $100. Real TiVo units run a Linux kernel, which makes these projects extremely cool to me.
Oh, and there's some comercial Widnows products out there too. Can't think of the names of them off the top of my head though.
* Your processor needs to be pretty quick if you're going to do any realtime compression and decompression. It's best to get one of those video capture cards that will do the MPEG2 compression in hardware so that you can free up your CPU.