Re: DVI out on my 6600GT
The OP is not as clueless as you might think.
There are 3 different versions of DVI:
DVI-A (analog passthrough)
DVI-D (digital only)
DVI-I (digital and analog)
Then there's single and dual link, but that only refers to the number of pins and available bandwidth for DVI-D. The key difference with DVI-A is that there is a set of 4 pins on the left side of the connector which pass through a VGA signal, the signal itself is not digital.
Older monitors and video cards were sometimes unable to show a BIOS screen, or anything before the driver initializes, via DVI-D and so the analog passthrough could still output a signal.
The OP probably has a DVI-I cable with the pins on it for analog and his TV is picking up that signal first. The 6600GT absolutely can do digital only, but it's a matter of his cabling choice in this case. I would get a DVI-D only cable (dual link, look for the full grid of pins) to try and force it. Otherwise his TV may have only had a DVI port for compatibility and is really only analog.