Our son won't be staying with us the weekend of the SXSW music festival so we're renting out his room. It's nothing fancy - bunk beds and a lot of toys, but hopefully it works for your needs! The bunk beds are big enough to fit someone as tall as 6'2".
The house is in chill, fun East Austin, about 1.5 miles from downtown. We're close to a lot of fun bars (Frontier, the Liberty, White Horse Saloon, the E 6th street bars), restaurants (Gourmands, Blue Dahlia, El Zunzal, Takoba, El Azteca) and SXSW venues. We're quite close to the number 4 bus line, a short 10 minute bike ride (or five minute cab ride) from downtown and just a few blocks from a grocery store.
You'll have access to a bathroom in the hall and can also use the kitchen, washer and dryer, WiFi, TV with DVD player, Wii and Apple TV (with Netflix and Hulu Plus). We have two sweet indoor/outdoor cats that you may seem roaming the house - they're quite friendly!
Note: during SXSW we also rent out the guest room and living room, so there will be a few other folks visiting at the same time.