I just installed Windows 7 Ultimate 64 RTM (from MSDN) on my HTPC, which is connected to a 42" Magnavox LCD TV via component cables to my nVidia 7900GS.
Everything was fine through the installation until I went to install the official driver from nVidia. Towards the end of the installation, the TV blinked off and wouldn't come back on. I went and got an LCD monitor and plugged it into a DVI port and the monitor came right up, but was automatically selected as the primary display.
Now, if I set the TV to be the primary display, the TV just blanks until I hit escape to cancel the "settings have changed, do you want to keep them" dialog.
Update: I'm able to set the TV as the primary display using the Windows 7 "screen resolution" configuration panel. However, if I try to remove the LCD monitor either by unplugging it or using the configuration, the TV blanks out again.
Update 2: This setup was working correctly in Vista Home Premium 32-bit.
Update 3: I've uninstalled the nVidia driver and am using the driver that Windows Update installed. As much as this offends my geek sensibilities (must use the "right" driver!!), well, It Works™.