Dual Monitor issues

i have a dell optiplex 620 with a ati radeon 600 128 video card that is using a slot 10(conmect to my monitor via vga). i want dual monitors( just duplicate the two screens) can i use the output from the motherboard (for my tv) and the ati in slot 10 for my monitor on the desk?......

i actually think it is a d sub connector??(maybe). it has 2 sets of 9 pins and 1 pin facing horizontally. i unplugged this cable( feeding to my monitor) and just plugged in the one to the motherboard(to my same monitor) and i get a message "this computer has an add in graphics card but the monitor is plugged into the integrated video connector." and has instructions on how to plug into my video graphics card. why wont my integrated plug work?? any help would be greatly appreciated.