Most versions of Windows Vista and Windows 7 included Media Centre, which allows you to use your living room computer as a TV tuner and audio/video player.
With the move to Windows 8, however, Microsoft has dropped Media Centre from the basic product, apparently citing the cost of additional decoder licences as the main reason for having to charge almost $40 for the add-in.
However, you can still get Media Centre for free if you upgrade to Windows 8 Pro before the end of January 2013. Just head to http://windows.microsoft.com/en-US/windows-8/feature-packs and enter your email address, and you'll receive the software plus a licence key.
Windows Media Centre makes a great TV and PVR (personal video recorder) combo. So it's definitely worth getting hold of a copy while it's free, even if you don't intend to install it right away.