Ever watch the Runoffs on Speed channel? This is a qualifying event for the SCCA Club Race national championship.
http://www.scca.com/Club/National.asp
You need a race license and a Club Race prepped car to enter. If you're planning to work the event, check out the SFR Flagging & Communication refresher course at Infineon (it's usually in February IIRC). You'll learn a lot about what it takes to work a flagger station at a race.