plugins/xrandr and uncheck the
"active" entry (Important, you will have to place a file with an
appropiate xrandr initial configuration in /etc/X11/Xsession.d/ a
sample is given in the link below).
You could also try a simpler xorg.conf. Try NO options for the external monitor and set everything up in the xrandr conf file
If you want more info, this helped me a great deal:
http://www.jejik.com/articles/2008/10/setting_up_dual_monitors_system-wide_with_xrandr_on_debian_lenny/
Unfortunately radeon in lenny couldn't handle using the 2 monitors at the same time well, so I opted to have a launcher on the desktop for use of TV only and one for use of laptop screen only. I don't recall if I ever closed the lid on my laptop after choosing only to use tv as output but I have the feeling I did try it. You could also go to System > Preferences > Power Management and choose "do nothing" or "blank screen" for the option of what to do when laptop lid is closed.
To try to solve these problems I ended up installing squeeze on that laptop. It works much much better. However, I still find the using of only tv / laptop screen appealing so I've kept the launchers on the desktop. I will try closing the lid.
If you have problems, please try getting a newer radeon driver from sid (you'll need a
newer kernel as well, either 2.6.32-10 from sid or 2.6.33 from
experimental). For this you will need to enable Kernel modesetting. add
radeon to
/etc/modules and put
options radeon modeset=1 in
/etc/modprobe.d/radeon-kms.conf (you'll probably need to create the file). I have this set up in the laptop and it works pretty well. (Please also get firmware-linux firmware-linux-nonfree libdrm-radeon1).
Hope this helps
Andres