if it is the same case that comes with your prebuilt then. no.
but if you give me your budget I can suggest the components for a new build, you can get a decent new case for 40-60 dollars depending on your preference, and you can build a decent gaming rig for around 500 dollars these days:http://www.tomshardware.com/reviews/phenom-ii-overclock-graphics-card,3032.html
check out Toms 500 dollar gaming rig^^^
If that is out of your reach then id start saving and deal with what you got now, possibly get a cheap gpu off ebay such as a 9600 gt or 4850