Matt,

Do yourself a favor and finance it. If you have basically no credit history because of your age, they'll offer you a horrible rate, but take it. Just don't accept any loan origination or other fees, and make sure there is no prepayment penalty.

Make your first two payments normally, then just pay the loan off in full for the third payment. Assuming that you make those three payments on time, this will do wonders for your credit rating. Not as much as paying the loan off in the normal time would, but the APR you're likely to get would make doing that more expensive than it's worth.

As an aside, another thing you can do is get a credit card with a low or no annual fee. Again, don't worry too much about the APR. Buy a few small things on the card every now and again. Don't ever charge it up to more than half of the credit limit, and pay it off every month to avoid getting raped in the wallet by the APR you'll probably have. Three or four times a year, leave $10 on it rather than paying in full, but be sure to pay it off the next month. Keep this card forever (which is why you want the low annual fee). Even after you get better cards later in life, keep this card open.

In the short term, simply having the card, using it, and paying it on time will do the same good things for your credit rating as financing your new car. In the long term, two of the items that figure prominently into your credit score are the age of your oldest credit account and the average age of all your open accounts. Getting a card now and keeping it open and in good standing will help with those two factors down the road.

Cheers,

Greg