From what i can find your machine only has 1 pcie 16 slot hence the dual card option isnt there for you.
I can't find details on what PSU you have either at present but the card i'd recommend for you would be this
It supports 2 screens is a decent card for running games on and isnt to expensive to buy.
For your info. alot of 2.0 cards will work in 1.0 slots.
I have a friend using a ATI 4850 in a 1.0 slot and it works fine for him.
If you have any doubts at all ring your PC suppliers help desk and ask them.