There are many places to take belly dancing classes in Austin. I will give you a few suggestions:
Bahaia (North Austin) - http://www.bahaia.com - She is the former organizer of the Austin Belly Dance Convention, and one of the best teachers in Austin. I have not taken lessons from her, but I have seen her students dance, and I have seen her dance, and she is hands down the best as far as I can tell. She also does her Hot Seminars and other events. She teaches traditional Raks Sharqi and Cabaret.
Stacey Lizette (South Austin) - http://www.staceylizette.net - The current organizer of the Austin Belly Dance Convention, and another of the most widely known teachers in the Austin area. She teaches according to Suhaila Salimpour