The program has gone by a number of names: Car Allowance Rebate System, Cash for Clunkers, or simply CARS. However, no matter what you call it, it went fully into effect at the beginning of this weekend.

The CARS program is surprisingly simple. If you have an old car with low gas mileage (under 18 mpg for cars, slightly different requirements apply for trucks), and you buy a new car with improved gas mileage (again, certain limits apply), you get cash back from the government towards the purchase of the new car. The amount of cash is significant, as well: either $3,500 or $4,500 depending on how good the mileage is on your new car.

There have been questions as to how the mileage of both the old cars and new cars are calculated, and what cars qualify and don’t qualify. Luckily, the CARS website provides an easy calculator to help you determine if your car is eligible. Just go to this website, and enter the information for your old car, and the new car you’re thinking about buying. The site will tell you whether or not you qualify, and how much money you’ll receive. The money is coming from the government, not the dealers, so most dealers will be happy to help you with this process as well.

The restrictions on the cars program are sparse and simple, and seem largely designed to avoid fraud without complicating the process for average citizens. All you have to do is provide proof that the car has been insured, registered and titled to you, and in running condition for the past year. (Also, you can only partake in CARS once.)

According to the CARS website, the “program runs through Nov 1, 2009 or when the funds are exhausted, whichever comes first.” I talked to a sales rep at my local Toyota dealer last evening. She told me that her dealership alone had taken in at least 40 clunkers over the weekend. At an average of $4,000 per car, those cars could account for is $160,000 of the allotted $1 billion, a significant amount for a single dealership in a single weekend. I’d personally bet that this money will be gone long before November.

So, go get rid of your clunker and get some good gov’t cash towards a new (and hopefully far more green) car!