7600GT supports dual monitor. And, as far as I know, every card from that one, at least, and upwards supports dual monitor.

Basically, you need a Serial to DVI adaptor. I have a feeling that one comes with the card to actually connect the monitor to it in the first place, seeing as the card doesn't have any serial ports (from my experience, the latest nVidia cards - 7600 to 8800 - have two DVI ports, and one D-SUB port). As for buying one, I haven't a clue how much it would cost, but I don't think it would be that much.