Hi,
As I stated before, your present Video Card is PCIe x 16 as is the new one. You will have at least one slot on your m/board.
Whichever card you select will need to be PCIe x 16. ( The vast majority are ).
Your PSU is 350Watt - if you are upgrading the Video Card you will need to upgrade this too.
I would suggest at least 600Watt - you would then have more than enough power if you decided to upgrade again.
Did you take a look at this one recommended in my link above. These guys know what they are talking about.
http://www.tomshardware.com/reviews/best-gaming-graphics-card-geforce-gtx-590-radeon-hd-6990,2879-3.html
You don't say what you want to use the Video Card for.
If it is gaming ( I am not a gamer ) then you could do a lot worse than to take a serious look at the link provided.
I stop at recommending specific hardware.
I leave it to you to spend your hard earned cash.
I hope I have helped you come to a decission.