You could spend a couple weeks in Central Texas and still have plenty of worthy places left to visit, but realistically you can experience everything the region has to offer in six or seven days. Plan to spend at least two or three days exploring Austin’s  cultural scene.
Devote an entire day or two to the area just north of downtown, home to the Capitol , Texas history museums, LBJ Library , and the Blanton Museum of Art . You’ll probably need two nights to take in the live music and club scene, and it’s worth devoting an afternoon to a Lockhart  day trip just to experience Texas barbecue at its finest.
Set aside another two or three days to drive through the Hill Country , with suggested overnight stops at a bed-and-breakfast in Fredericksburg or a dude ranch in Bandera. Fredericksburg’s  German heritage offers a memorable getaway, and it’s downright sacrilegious to be in Texas without experiencing “the Cowboy Capital of the World,” as Bandera  proudly bills itself.
Other worthy Central Texas side trips are Bryan-College Station  for the George Bush Presidential Library and Museum  and the whole Aggieland phenomena, San Marcos  for floating on an inner tube down a river, and the Highland Lakes  for more traditional water-based recreation.