I just came from the store after buying a second monitor to dual screening.
I installed an ATI PowerColor 6850 GPU on the Asrock G41M-VS3 R2.0 MOBO. The GPU has two DVI slots, I use adapters for both VGA monitors. Both monitors work fine in the first slot (along the plugin confirmation sound). And if I connect any of both monitors to the second slot I won't get anything, nor a signal or confirmation sound.
I also tried auto detecting via Catalyst Control Center and Windows Desktop Resolution. I have the latest drivers installed.
Although AMD GPU's comes with 2 x DVI ports, one of them is DVI-D (Digital) and the other is DVI-I (Analog). The DVI-I is the one with 4pins around the flat PIN in the DVI. The 4 PIN is for the analog to which the DVI to VGA adaptor connects.
So if you put a DVI-VGA adaptor to the DVI-D, there is no 4PIN to which the adaptor will get the analog signal. I wonder how your adaptor fits into the DVI-D because in my experience, the DVI to VGA adaptor have the 4PINs which do not have the holes to go thru in the DVI-D port.