I have 2 cards (ati) both will do this. in 2 differant ways.
clone desk top. = both screens are the same ( this was very handy when I 1st built my cabs) cab #1 was horizontal cab #2 was vert. 1 pc. in mame I tab the vertical games to flip and work on that CP and horizontal to play on tv.
just do a side step and play what you wanted.
extend desk top you have 1 desk top extended on 2 screens. I found this hard to work with. Others seem to like it.
If your TV has composit out like mine has you can have 3 screens or like the card in this pc I have 2 VGA and 1 s-vid , I had to try it just to test and all 3 work at 1 time