I've run into two lines of thinking on cars when the 0% option is offered. One is that you should buy the car with cash - always. Car debt is not usually considered "good debt," as there is no doubt but that your car will depreciate. Unless something very odd happens or you keep the car to antique status (and it's a good one), you won't make money off of it.
On the other hand, with 0% interest - if you qualify, and remember that dealer promotions aren't for everyone, just those who qualify - you can invest that money in a savings account, bonds, a mutual fund, or the stock market and theoretically make a lot more over the 5 years while paying down the car. In that case, you really only need to make sure you save enough to make the payment low enough for your comfort zone.
Personally I prefer to not be making a car payment. Your personal comfort level may vary.
Also, in terms of getting your money's worth a gently used car in good condition is miles better than a new car. Someone else took the hit on the "drive it off the lot" decline in price for you.