Matthews Planet Preowned Had car 7 months now and in that time have but over $1000 into it. vestal, New York

We purchased a car from Matthews planet preowned in December of 2010.  My husbands car got totaled and we needed a new vehicle quickly so we went to Matthews as they said they could help us out.  When we got there they had a 2000 Saturn Sl that they told us we could get and it looked like it was in good shape so we purchased it.  This was the worst decision we made. 
A month after we got the car the ERG valve blew off the motor and it cost us $400 as the insurance they had us purchase with the car didn't cover it.  Matthews sent us a "good will" check of $150.00.  Then my husband kept smelling gas we took it to a repair shop and the gas valve was rusted.   We called the insurance place as they didn't cover the ERG valve and they told us they cover the motor and transmission so we cancelled the insurance as we figured why pay $2000 for something when we had to keep paying for the repairs anyway. 
We thought that was that...but no the car would start but not go into gear so we called Matthews and they said really nothing they could do we cancelled the insurance.  Rob Matthews called me back and I told him what had been going on and that we hadn't even had the car that long and he made it so we only paid the price for the computer and no labor...still over $300.00 and the $75 for putting it on the machine. 
Was that the end???  No, the car isn't starting all the time and when we took it for an oil change it needs a spring and the boot(?) as its leaking which the garage said would be about $400.  I have to tell you honestly that yes my husband has lost his temper when he went in and wasnt very nice but I can't really blame him for that as we have done nothing but put money into this car and still pay the payment on it every month.
So my final call to matthews was 8/3/11 when I spoke to Mark and yes I did send an e-mail to the tell it to Teresa on their website telling them how unhappy I was and I tell you this because Mark kept saying this over and over...I asked them very politely to please get us a different car as we just can't afford to keep fixing this one...the reply I got? Sure come up with $3000.00 to do the trade in and for a downpayment LOL If I had that I would have went to a different dealer!!! We are upside down in this car as we owe more than the trade in and that was even after we received a refund for canceling the insurance!!
So we are stuck with a car that we keep dumping money into and I really really want to go park this car in their lot and walk away but the only ones hurt by that would be us with our credit...they already got their money why do they care?