Clyde n Deb,
Tincup703 is correct about simply purchasing a Sirius receiver. It would however be external to your built-in XM receiver that came with your TV.
Posted below is a link to the status of the XM/Sirius merger with other links from there that may interest you including what the merger will accomplish, pricing and satellite station selections.
http://blog.wired.com/music/2008/02/...-and-xm-c.html
My guess is the XM receiver you now have in your TV will be compatible once the merger is activated with Sirius programming that you will be able to choose. Good Luck