an HTPC, and yes they function as a DVR and are quite easy too build. Here let me link you to an how to for you doubting thomas.
http://www.ramelectronics.net/html/HTPC.html
http://www.engadget.com/2006/01/24/how-to-build-a-practical-htpc/
http://www.firingsquad.com/guides/building_home_theater_pc/
This is just the first few links on Google. Maybe you can do a little investigation yourself before coming to some uneducated response again.
just to be sure, I was half kidding when I made my remark :))))) ok?
But, the point is, since I have 3 dvr's and since I seem to hate commercials EVEN MORE as time goes by... I might even try to build something just for that purpose.
So, I would love to hear from someone who has actually built one of these things.. or can ask someone who has done one... you know, just to save time... Thanks