Yes a pci express card will work with your current motherboard, I would say a gtx 550ti or gtx 560 is a great starter graphics card, unless your looking for something like running Battlefield 3 at 1080p resolution with maximum settings(only a few very expensive single graphics card can do that right now), Also the gtx 600 series is a few months away but if you don't want to wait go with the 550ti or 560. A word of advice on using a manufacturers case, I use a manufacturer case for my computer now, and the cooling on it sucks since they don't expect people to be putting graphics cards in there, plus there is no place for fans unless you mod the case, looking at pictures of your computer online, your case appears to be the same way, only one place for a fan, this is fine for the winter, but when summer comes around you will experience some cooling issues mostly while playing games and sometimes when your doing other things. If you don't have money for a new case, I have lived on my manufacturer case for 2 years now but had to use external cooling sources for it to stay cool during the summer(like regular fans). But I would highly suggest buying a new case once you have the money to do so, or right now if you can.