If it is bad (below say 600) there are lenders out there that will still help you. In exchange for a good credit score, you will most likely pay higher percentage, extra insurance and/or points (fees) to get a loan. Loan are all risk based. If you have compensating factors such as a large down payment, many assets, etc, then it may help you to qualify. I would suggest trying to work with a broker who works with wholesale lenders and not retail lenders like Chase or BofA as they are not flexible or able to modify their loan programs.
Hope that helps some.