Any number of tuner cards come with their own DVR software.
My AVerMedia USB tuner has it's own DVR software - or I can just have Media Center do the DVR work.
Getting other than OTA or ClearQAM(cable) HD to the PC may be a problem.
Hauppauge does have a component to PC device($249 I believe) that can accept feeds from a cable box.
http://www.hauppauge.com/site/products/data_hdpvr.html
Pretty sure it comes with software.
EDIT: $207 at Fry's:
http://www.frys.com/product/5636821?...H:MAIN_RSLT_PG