You can sell your car, apply for a car loan with bad credit and add the amount that you have for the down payment of the car. These car loans will give you the money that you need and they will pay it for you, but you have to pay it to them installment with interest. http://quickyloan.net/ might give you some advice about this.
U can negotiate with someone who has good credit (relative) an have them co-sign or go a cheaper independent dealer who takes trade-ins and trade your car with them (those type of dealers normally doesn't stress over bad credit) stay away from car-max
Depending on the make/model and condition of your car you should be able to trade that in...I would suggest trying to save "some" money towards a new car..the fact that you have bad credit is a clear sign that you do not take care of your debts so any friend/family member would be a fool to risk their credit just so you can drive..save some money and see what the car you now have is worth...it's best to stand on your own two feet when making a major purchase like this.