If your credit is bad, it really depends on how bad. Credit scores below 580 are not getting approved often if at all. Between 580 and 620 it's technically possible, but tough. As the scores go above this the odds of approval improve and so do the rates.
It may be a good idea to start by working on improving your credit. Pay all bills on time, keep your balances low, pay down any large accounts and address any errors that may appear on your credit report.
Down payment is also helpful in getting approved with low scores, the more you can put down, 10% if you are around 580 to 620 the better your chances are. I hope this helps.