External monitor over the air with Macbook
Those extra four pins on your DVI to VGA adapter actually carry the VGA signal; the adapter doesn't actually do any adapting. (The terminology is: DVI-D is digital-only like your mini-DVI to DVI adapter, while DVI-I carries both DVI and VGA, like your cable.)

The hardware solution is to get a mini-DVI to VGA adapter (from Apple or elsewhere).