When I was at my Lexmark dealer two weeks ago, we were discussing credit requirements for Shefield to get the 0% for 48 with 6 months same as cash. He looked it up in his book and it said they want a 720 for top tier financing. With my scores currently between 690 and 700, I wanted to make sure I knew where I stood. He said that I may not get the 6 months of no payments, I should be able to get the 0% with my scores.
Having re built my credit over the past 2 years from a 498 to 700, I am very familiar with the credit rating systems, the different scores (currently 3 different ones from trans union alone) , different reports, what to do about them and I now watch my scores like a hawk. Not an expert, but I learned alot more about this topic than most people have ever thought existed. Unfourtunately, with a score around 500 you may not even be able to be on the loan even with a cosigner. At 600 I was able to get a usable credit card, at 700, I have over $30k in available credit lines not including the Amex that doesnt have a limit. Bad credit is worse than no credit. get a copy of your credit report and see what the problem is, if its an error, then it may be an easy fix and your scores will jump huge amounts when fixed.
Do yourself a favor and learn about credit and how the scoring works. Learn about the laws (FCRA and FDCPA) and how they can help you. A great resource is the forums at myfico .com.