Can I use an existing account?

I purchased a new Ford in 2006, with absolutely no credit. They put me on a first time buyer's program, and Ford Motor Credit financed roughly the entire cost of the car. For the sake of the question, we'll say it was $17,000.

Since then, I have made all of my payments on time, and have a good credit score (over 700 fico). On Thursday, I was involved in an auto accident, and my car was totaled. Insurance is going to give me the value of the car, and it's looking like I'll be between $1,000-2,000 upside down.

So here's my question: If I have a $17k credit line with Ford Motor Credit, can I use the line of credit in my currently open account to purchase another Ford? I've been told that my upside-down amount will roll into my new loan, and I'm totally okay with that. I am looking to purchase a pre-owned vehicle- will that change anything?

My husband and I are currently in the process of purchasing a house, and we have already been pre-approved for a loan, so I'd really rather not close any accounts or open any new ones if it isn't absolutely necessary.

Thanks in advance for your help. :)