if i want to get car with monthly payment do i need to have social security number?

It would help on less you want to pay severely high interest rates. Apply on line for a SS #. But do.it quickly, the winds of change are in the air.

i do not have one, because i am international student in ISU but i am going to paydwon $3000? what should i do

Look for a BUY HERE PAY HERE used car dealer. Since your here legally you should be able to get a decent vehicle. BTW what state are you studying in?

Idaho Sate , Also i found the car which i am looking for and that is (2005 Mercedes-Benz C-Class 4 Dr C230 Kompressor Supercharged Sedan)

Is the Mercedes being sold at a car dealership? If so they may have a source for 2nd tear financing. If it's a private sale then it's probably not going to happen. Did you get anything like a tax identification number? When you have time check out the finance companys in the city you are living in.

new in America and already acting like a Native- your eyes are bigger than your wallet- why do you think that buying on credit is a good idea? - have you heard of compound interest? why do you think you need a crappy used Mercedes to make your way through American life- if you don't have enough troubles already, go ahead and think that the American Dream is being in debt to a sketchy used car dealer and paying for the many expensive repairs that a used Mercedes will need- just so you can feel important- or get smart and buy a $3000 Toyota that will treat you right-

A "buy here pay here" kind of dealer has crap cars and high interest rates. They prey on poor people. In your situation you need to buy a car for cash. You're a student, no one expects you to be driving German luxury. Try to act with reason and not so much emotion. You will get more respect.

A.A. what are the mileage and how much do they want for the Mercedes?