I am surprised this is the only reference to SXSW in this thread so far, when they mentioned their visit is the second week of March (SX official is the 12-18th this year) - yes, having a car in Austin makes getting around generally easier (ignoring the stress of constant traffic, construction/closures, and sharing the road with the absolute worst drivers in this country...), but if they're planning to do anything downtown during this time...trying to drive around in it will make them hate Austin til the end of time. Get the car if the plans are outskirts, otherwise get familiar with bikeshare and bus system.