I believe the balloon amount is 37% (With teir one credit) x MSRP. You do not factor in what your final cost for the car or down payment. That's what the dealer told me when I was going to order a 335i coupe in December.
Now with the 335IS coming out, I'm on the fence if I should go after a 6,000 - 12,000 mile fully loaded 2009 M3 instead. It will be close in price.
Now I'm curious to know if BMW Select is offered on CPO.