The analog signals used by VGA are present on the ADC socket. The problem folks usually run into, is that almost none of the ADC<=>DVI adapters propagate those analog signals the DVI analog pins.

So a combination of ADC > ADC/DVI adapter > DVI/VGA adapter usually does not work.

It should be relatively trivial to open up an ADC/DVI adapter and connect up the analog pins at both ends properly.