This probably is moving away from what davidw was asking, but here's my quick guide to Austin.
The 6th street advice depends on who you are. If you are looking for live music, definitely 6th St. and the clubs on Red River. If you want cheaper drinks (like $1 Rum and Cokes of low quality), want to party with more of college-age crowd, are single and looking for attractive women, you will be very happy there. Very little work gets done on 6th St (unless you work in one of the bank buildings). Once the 6th st. crowd graduates, they hang out in the Warehouse District, which is around 4th and Colorado/Lavaca. This is where you go if you want more like a $4-5 drink or if you enjoy sipping Lattes. Less live music stuff. More cafes. I work out of a couple coffee shops over there, and also work out of a neighborhood called Hyde Park (which is not downtown). Austin is growing fast. There are many condos being built in the downtown area, particularly in the area that is now being called the "2nd Street District". Hyde Park is a cool little neighborhood if you don't want to hang out downtown. Houses are older, smaller, and more expensive there. When I say expensive, I mean Texas expensive, not California expensive.
I'll be at SXSW if anyone wants to meet up. I'll be attending the SXSW interactive and as many of the live music shows that I can fit in. The full list of over 1000 bands was released today and can be viewed at http://2008.sxsw.com/music/festival/alphalist/. Yes, all of them in one week.
For some funky shops and a cool place to visit in the day it'd be worth stopping by the South Congress area.
For live music places, I recommend Stubb's, Emo's, and The Parish Room (for more Indie Rock stuff), Elephant Room (for Jazz), Mohawk, and Antone's.
For a cool neighborhood pub with a jillion beers that you probably wouldn't run into normally, go to http://www.draughthouse.com/. Other places with a large beer selection where you can hear yourself talk are The Ginger Man and Opal Divine's.
Some magazine voted Alamo Drafthouse the best movie theater in the country. It's one of those theaters where you order a beer and food while you watch the movie, so I enjoy it more for a humorous movie. Some other magazine voted Book People the best bookstore in the country.
For good coffee places to use free wifi, go to Austin Java (Downtown), Halcyon (Downtown), Epoch (Hyde Park), Quack's (Hyde Park), Flightpath (Hyde Park), The Hideout (Downtown), Metro (by UT Campus), JP's Java (near UT campus), Little City (Downtown), or Spiderhouse (near UT campus).
Barton Springs and Zilker Park is where a lot of people go for outdoors stuff like running, walking dogs, frisbee golf, and swimming.
Shop at HEB for a big cheap grocery store. Go to Whole Foods or Central Market if you want to stock up on organic expensive stuff.
If you are rich and want to buy some designer sunglasses, go to the Domain or the 2nd St. District. If you are an indie/emo kid, go to SpiderHouse, Beauty Bar, or....Emo's. If you are a metalhead or goth type, there are some places on Red River for you.
For a really big delicious burger or some tasty wings, visit Casino El Camino on 6th. If you want some cheap gigantic breakfast tacos, go to Juan in a Million. For an open-faced burger with a mound of cheese fries piled on top, go to Hyde Park Grill. For a wine bar, go to Vino Vino.
A car is not very important if you know the Capital Metro bus routes and stay central, which is where most of the interesting stuff is anyway.
If you like bumming around a college campus, hang out around UT-Austin, which is between 26th and 21st st. Many people will be wearing an ugly burnt orange color, similar to the orange at the top of this web page.