Do you have a loan to pay off with school A or is it an actual bill? If it is a bill you will need to obtain a private student loan to pay it off. A Stafford loan will not cover this.
http://www.privatestudentloans.com can help you determine which private loan is best for your situation.
If you have a loan with school A that you need to pay off you can defer your payments while you are in school. You will just have to show your lender proof of enrollment on school B.
If you need a Stafford loan to attend school B you can file a FAFSA and apply for financial aid through the school.