from your description, I assume your card has two DVI connectors.
Please check the documentation (or ask the manufacturer of the card), which kind of DVI interfaces are used. To connect your VGA monitor, you need DVI-I (or DVI-A) connections. Any inexpensive DVI-I to VGA adapter should be fine then.
Maybe this is helpful also: http://en.wikipedia.org/wiki/Digital_Visual_Interface