What you can do is get a TV Tuner card for your PC... I'll provide a link of a sample TV tuner card below. From there you can either use the software thats provided or use Windows Media Center to record the tv shows wanted. One great feature about Media center edition is that it has a built in TV guide (like digital cable) and you can set up shows to record if you're not going to be around with much ease! If you need more information let me know...
Here is a link to a tv tuner card
Newegg.com - Hauppauge WinTV-PVR-150 MCE 1042 Tuner Card - Retail