wel i got the car from the dealership,which was already overpriced as it is. I got the call for 17100+, than financing knocked it up tp 21K

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Maybe you should lay off some of your namesake stuff, man.

I only paid $2,000 more than that when I bought my fully-loaded '03
brand-new.
Looks like you're gonna be stuck with the 6 for a while. At normal payments you're looking at paying down for another 3 years before you come up even on the trade and can even realistically look at replacing it with something else.
One other thing to remember is that most major lenders have a rather low allowance for what they will allow you to roll into a new car. Meaning, you can't go buy a $15,000 car and roll in the $7,000 that you still on the Mazda6. Aside from that just being dumb a good lender isn't going to loan that to you. There's too much risk if you default on the loan. The bank will be stuck with a car with $10,000 and a loan on it for $22,000.
Roll in anything more than 5% of the value of the new car you're buying and they're gonna start looking at jacking up your interest rate. Anything more than 10% and you're certainly looking at a 1-2% higher rate. More than 15% and you price yourself out of prime lenders and you probably cost yourself another 2% or more. More than 30% and they probably wouldn't give you the time of day unless you had really good credit or they
really wanted to sell that car.
To stay in that tolerable-but-still-not-smart 15-20% range with $7,000 in negative equity, you'd have to buy a car with a purchase price of about $30,000.