I had a Green Button remote provided with HP PC XP, Vista for Windows Media Center prior to getting Mac Pro.
Now in Lion, I have Hauppauge WinTV HVR-980 USB adapter (less than $100) including a remote that works in Lion for the Hauppauge TV app.
In Windows, the same remote works with all "Media Center" processes Music, Pictures, TV... instead of mouse/keyboard. If your TV service requires set top box, then you have to use its remote to change channels.
If ISP's internet Co-Ax also carries TV signal, you can get Cable Splitter (smple picture):
http://www.ebay.ca/itm/2-Way-TV-RF-Coaxial-Cable-Splitter-CATV-Signal-/320868649 227?pt=LH_DefaultDomain_0&hash=item4ab543090b
and feed 1 co-ax to USB TV adapter, the other to your Modem/Router.
The Hauppage USB was a good choice because it serves Mac & Windows.
Also, In Windows, if you have an XBox, it can be used as "Extender" for your A/V output.
http://windows.microsoft.com/en-US/windows7/Set-up-a-Windows-Media-Center-Extend er
Although this may not answer your question, it describes other options.