I heard a lot of people saying the DM9 cant mirror, but thats what I got it doing though VGA to VGA input on my Toshiba 40" LCD HDTV.
I first tried plugging in the LCD to the DM9 with a Dell EFI 1.25A on Leopard 10.5.7 install, but it would only show me a garbled mess. I then downloaded the Dell EFI 1.25A installer to install the "old GMA mirror friendly kexts" but on reboot the issue persisted. I then ran the Dell EFI 1.1 installer and checked the "old GMA..." box, rebooted and I could now see the LCD show an extended desktop. I then rebooted with the LCD connected and it boots with the desktop mirrored on the LCD and a black screen on the laptop. Its awesome! I will make a new thread with pics later.