Ms. D likes to point out that I'm less of a car reviewer and more of an obsessive car shopper. She's right on many levels—while I like to take sports cars out for a spin, I don't quite covet every muscle car that comes down the line. I like a lot of cars, and I enjoy driving just about anything different. But what I really like is the idea of getting a good deal. I like a car that's practical and efficient and affordable at the same time. And I'm a bit of a sucker for that new car smell, too.

So, I've been closely watching the selling frenzy that has been the automobile market in the past two years. With the economy in the tank, it seems that nearly all manufacturers offer something approaching zero-percent financing as a rule—or they offer stupendous lease rates or considerable rebates. Those numbers have continually taken me back to the Web sites of my favorite cars, where I use the Build Your Own function and run the numbers through their calculators to see if the payment looks good.

Recently, however, I realized that I'd been looking at things a little backward. What the financial planners tell you is to think more about what you're paying for the car in total and less about what you're paying each month. While many of the online calculators will help you fit your payment into your budget, it seems that the pros will tell you that it's more important to fit the car into your budget.

Some of that I already knew. But one thing that's simply worth remembering is that the car payment itself isn't magic. Sometimes when you look in the paper, it seems that an unbelievable low payment has popped up. But if the payment seems too low to be true, it probably is—you're paying in large down payments or balloon payoffs. Or, maybe you're looking at a car that you could get even cheaper.

The law of payments is even easier to see once you get down to zero-percent financing. At zero percent, you'll pay $16.67 per $1,000 that you finance over five years regardless of the make or model of the car. There's no way to make 60 payments lower than $16.67 per thousand at zero percent. At that point, the only way to make the payment cheaper is …to get a better price on the car.

Two things are interesting about this. First, to minimize the payment you make, most financial gurus recommend that you buy used cars. That was true of Charles Givens back in his 1980s heyday (before he got in trouble), and it's true of radio-guy Dave Ramsey today. Ramsey is particularly adamant about focusing on whether you can afford the car instead of the payment, and he recommends specifically against leasing a car. (In fact, he recommends pretty much against any credit except a mortgage.) Of course, many of us know that buying a used car means that someone else has paid for the depreciation that happens when you drive the car off the lot.

But let's say you're stuck on buying new. What may not be clear in the current selling climate is that choosing the zero percent isn't always the best scenario. This is particularly true of cars that offer the big "or," as in "cash back OR zero-percent financing." That cash back may be something you're not even considering because you want the lowest payment. But, remember that the only way to make a car cheaper is to get the price lower.

For example, GM right now advertises $4,000 cash back or zero-percent financing up to 60 months (for buyers who qualify) for a Pontiac Sunfire. (Not my favorite car—not even my favorite Pontiac—but the deals are best on the less popular cars.) For the Sunfire, the price is $15,495 for a base model. Assuming you could get out of the dealer without haggling, trading in anything or putting a down payment on the car, the payment would be $258.25 per month at zero-percent financing and the total paid is $17,045.

But what if you take the $4,000 cash back? Again, assuming no other haggling, trade-in or down payment, the best you could do at PeopleFirst.com (on the day I wrote this) is a 3.99 percent loan. But you'd be financing $11,495. Result? $211.65 per month for 60 months, and your total payment for the car is about $12,670. (Of course, that's for folks with the best credit—but, then again, so is the zero-percent deal.)

And the truth is that you might get an even better price if you walk into the dealer with your financing already squared away—or at least an idea of what your bank will do so you can challenge the dealer to beat it. As the 2004 models start to roll out, you might be able to get a good price on a 2003, then get the rebate and make the transaction easy for the dealer because you're handing them a bank note.

It's not the only way to buy a new car—and it works best when you're getting a serious cash incentive—but it's food for thought. If you shop for your loan ahead of time at your credit union or online, sometimes you can even piece together a deal that beats "zero." And that would be a good day.