There are a lot of details when it comes to the "Cash for Clunkers" program! If you're thinking about it, click here for the best (government's) resource.
You'll also want to see if your car qualifies. Click here to see if it gets 18 mpg or less.
The vehicle you trade in for has to have at least 22 mpg or if you're getting a truck or suv, 18 mpg.
You'll get 3,500 dollars (voucher) towards your new vehicle.
You may get 4,500 dollars if the new car gets 10 mpg better than your old one, or if your truck or suv gets 5 mpg better.
This is not going to be a good deal if your trade in is worth more than the voucher. If you use the voucher, you don't get anything more for the trade in value (by law the clunker has to be destroyed).
This program goes into effect now, but many dealerships are waiting until the end of the July when all the details are going to be issued.