Auto Loan Questions: What determines the loan term (as in 12, 36, 60 months...)?

I am trying to get a loan for a car and havent had a loan in quite a few years. What determines the term of the loan - as in how long you have to pay it back. Is your credit rating the main factor, or is it your own decision? Also, my credit is not that great. The only issue with it is a credit card I never paid on - it went to collection & last I knew, I owed almost $900 to pay it off. I havent heard from the collection agency in a long time - they didnt send me anything or call for almost 2 years, then I recently received a letter trying to collect on it - mistakenly, I lost it & now cant even find out how to reach them as I dont know the name of the company (tried getting my credit report - already got the limit for the year though & didnt keep a copy - stupid I know). SO, does anyone know what the chances are of me getting a loan? I already know that if i DO get a loan, the interest rate will be high. BUT, I NEED a car as mine is about to blow up. Any advice?