TexasGurl,
Underground is fun for the history, there are lots of varied shops, and quick dining, and some restaurants. The nightlife area is Kenny's Alley: http://www.underground-atlanta.com/nightlife/kennys-alley.html
Everyone's taste is different and there might be some other nightlife areas you might like to try also like Atlanta Station which is in midtown.http://www.shopatlanticstation.com/
You will not recognize Atlanta, and should have a blast.