Beginning at 8AM on Thursday there will be street closures for the First Night Festival that will affect routes you may want to take to get to the IKKiCON hotel. In particular, Cesar Chavez will be closed the entire day.
At 5PM additional streets will be closed for the First Night Parade. Most importantly this includes a portions of 5th St and Congress. After 5 PM you’ll probably want to take Enfield/15th past Congress if coming from the west.
This is a closure schedule for the event: http://www.ci.austin.tx.us/specialevents/downloads/firstnight_123109.pdf
This is a closure map: http://www.ci.austin.tx.us/specialevents/maps.htm