Is it this one
http://www.newegg.com/Product/Product.aspx?Item=N82E16813128394 ? If yes then it has PCI-Express 2.0 so you're fine installing any new gpu in it, maybe like ATi 7950 or 7970 depends on your budget really and free space in your case if you have one. P.S. it will close that PCI slot with itself just a note if you have anything in there.
Ok thanks. So pretty much nothing bad could happen with any gpu? I have 700w power supply and 4gb ram
Yep, that psu is more than enough and what about ram it's fine for mining but if you are using computer to play games or to do any other stuff I would recommend to have 8, but 4 is good enough pretty much.