I am Australian and I want to move to America, How long will it take to get my permanent residence?

I am currently living in Australia and in a coupe of years time i am going to move to the Unites States, How long will it take for me to get my Green Card/ Permanent Residence ? I have tried to find the answer to this but i cant, some people say it takes about 4-5 years to get one but that is just for Mexicans. I will be getting a student Visa. Please Help !! Thanks (: