Well, you can only really deduct the payments if you are an independent contractor. And then, you can only deduct the payments equal to the business percentage.
For example - say you put on 2000 miles a month on your car. 1000 of that is business, a 1000 of that is personal. You can only deduct 50% of the costs (payment, gas, insurance, tags, maintanence, ect).
If your car payment is $400 a month, you can only deduct 50% of that + other expenses. The alternative is to just do a milage reimbursement. Right now it's at $.365 per mile. So if you drive 1000 miles a month, you would be reimbursed $365.