How can I use my computer hard drives to use as a DVR?

Practically though those drives are teensy, too small for practical DVR use.

Wipe them and donate them to organizations that refurbish computers for charity. They are big enough to hold a basic OS and apps. I have an 80GB drive in my older computer.

You mean you want to pirate TV shows? This is what Hollywood thinks you are going to do which is why they make it tricky.

You basically need a TV tuner card for your PC and you plug in either a coax connection from your cable system or hook up an antenna and have it scan for channels. There is software you purchase or software that is free but you pay a monthly fee for the electronic program guide that your computer uses to record shows at scheduled times.

You want to search for "PC based DVR" for sites with software and instructions.

But remember - what you want to do is the exact same thing that pirates try to do so there are lots of blocks to doing this.