If you have an old car and want to get some Obama change to trade it in for a Prius, The New York Times has a helpful primer that explains the details of the federal Cash for Clunkers program. An auto is only eligible for the $4,500 rebate toward the purchase of a more efficient vehicle if it’s less than 25 years old, has an original mileage rating of under 18 mpg and it is in good driving condition. Other useful info: don’t assume the dealer won’t give you other discounts (haggle as you would on any new car purchase) and move quickly; The $2 billion in additional funds may only last a few weeks. For more, read the full story in the Times.