Infrared (IR) hardware allows wireless communication and data transfer between devices by the transmission of infrared light.
In case of Windows Media Center if you have a Set top box,a Media Center compatible remote control and IR devices you can change the tv channels.An infrared remote control cable—also known as anIR blaster—is a small, infrared device you can use to control a cable or satellite set-top box using your Media Center remote. These are generally packaged with Media Center remotes and TV tuners.
To know more:-
http://windows.microsoft.com/en-US/windows-vista/Set-up-a-TV-signal-in-Windows-Media-Center
S.Sengupta Media Center MVP