Radeon 7500 + TV out: xorg.conf settings?

[David Hagood]

I am trying to set up the 1.3.0 X server on a Radeon 7500 to support
both video on the VGA and on the TV port.

I have TV out working if I use xrandr to set up the display:
  xrandr --addmode S-video 800x600
  xrandr --output S-video --mode 800x600

However, what I would like to do is to have this come up automatically
when X comes up, *and* I would like to have the TV display be a separate
sub-screen with its own (region of the) frame buffer.

In other words, I want to have the VGA monitor being :0.0 running
1024x768, and the TV out being :0.1 running 800x600 (NTSC), so that I
can stick MythTV on :0.1 and let the normal desktop be on :0.0.

Is this possible, and if so, what do I have to put into the xorg.conf to
make this happen?

Alternatively, what would I have to put into my X startup to make this
happen?