Question about PC on a television

[Fred Forsythe]

I recently built a new pc & have set up a television in another room to view pc based videos on. I have an ATI card, the software has a nice feature that allows you to configure the resolution & refresh rate for both your monitor & the television separately, the TV is connected to the PC by running the s-video output of the vid card & the audio from the sound card into an RF modulator, which then conveys the signal across the house to the TV via some coax that was conveniently already in place. I all works quite well, I can view all variety of video files (mpeg's, avi's, vob's) as well as streaming video on the set with very nice quality. One thing seems odd however; although I don't really have a need for it right now, I had expected that ANY image which was showing on the pc monitor would also appear on the TV. When I am not playing a video on the pc (in Video Lan's VLC, Windows Media Player, Nero, Real Player, etc) what appears on the screen is the image I have on my desktop. This is regardless of what is actually on top in the PC window at the moment (e.g., if I have Firefox or Word or whatever open, still the image in the TV is the desktop picture. Only time a program is displayed on the TV is when I am actually playing a vid file or streaming video). Why would this be?

TIA

Fred