is it possible to get into a car with just a 700 hundred dollar down payment and poor credit

Not likely. Truth is CarMax financing is high for people with good credit. I would consider saving more before buying anywhere.

I was looking for financing but i am not trying to pay more than 225 a month

I'm not sure you have to put anything down if you're financing....

Not sure....never bought a car from Carmax before. You might want to call them, before heading over there.