I will explain my problem: I have an nVidia video card that can output to an TV (GeForce 4 MX), and I have an TV, 10 meters far from the computer, conected to the card. I would like to decode videos with a program (xine, for example), output the image to the TV, and have the xine control panel displayed on my primary monitor (the one besides the computer). It seems that neither TwinView nor Xinerama is suited for my purpuse, since I do not want to split my desktop beetwen the two screens. I am using X.Org 6.8.2 configured with 2 separated screens. I believe that to achieve my goal, I would need to do something like activating the XVideo extension and directing the XVideo output to the screen that represents my TV. The problem is that I don't know anything about XVideo (except that it is deactivated on my box), I don't even know if what I want to do is possible.
I have a problem with XFree that I cannot find any info about it: I did not find anything about how to set up DGA when I looked for it, as I cannot find any info about XVideo now.

xvinfo says:
Xlib: extension "XVideo" missing on display ":0.0".
xvinfo: No X-Video Extension on :0.0

If anyone knows how to do what I want to, or knows where can I find info about XVideo, or knows that it cannot be done, please tell me.

It is infact Xinerama that you want, and use the TV as an extension display. Just make sure you put the TV logically above the main monitor if you can.