If you’ve got an old laptop sitting around, you can fairly easily turn it into a barebones media player with this detailed instructional post on Engadget. Please note that I said “media player,” not personal video recorder.
Essentially the process involves installing a freeware program called GeeXboX on your machine. You will want a machine that has some sort of non-PC video out, and the article points out that if you are lacking the appropriate hardware, you can purchase a mini itx box for around $200 that has all the hardware you need in an extremely small form factor.
Pretty cool for not too much dough.