its really simple, just take your second monitors crt plug, attach a crt to dvi adapter and then attach it to your card, then boot into windows, right click on the desktop-properties-settings, configure it in there
Just plug both in. It should run whatever is in the VGA connector. Then from there, set up the second montior by going to the desktop/properties/settings and set the display. It doesn't matter what card it is (nVidia nor ATI)... well, from experience.