All you have to do is:
1) be Australian
2) be 18 or older
3) vote for your favourite user-submitted commercial for Just Car Insurance
... or you could make and submit your own ad for a chance to win $10k, but that requires effort, so meh :p
Check out the link below for the FULL details!
http://www.justcarinsurancereeldeal.com.au/prizes?cmpid=JCI:GI:PI:CAR:DIS:20110701:078