Yeah, the Geforce 7100 is actually an IGP... and not even a new one. Any sort of dedicated card would be an improvement (or practically any card- to be more specific, any PCI express card). With your current IGP, you can't play anything. However, for $70 you can pick up a Radeon HD 6670, which can draw all its power from the PCI Express slot (assuming you have one), and will provide entry level gaming options. http://www.newegg.com/Product/Product.aspx?Item=N82E16814102988
I would recommend doing a little research, and if your system supports it, picking up one of these (or maybe a little higher- depending on your budget).