Radio Shack does on any purchase over $199, But it's really just a credit card that can only be used at RS. Ebay has financing on anythng over like $200 or 250, but again I think it's just a credit card through PayPal.
Plenty of them do. You send them 50 low payments of $10, and upon receipt of the 50th payment, they send you the scanner!
Seriously, look at it from the retailer's point of view. There's so little markup in scanners these days that if you offered them on a "rent-to-own" basis it would be easy for one deadbeat to kill any profit margin you might have had. No one's going to take that sort of a risk. Besides, if you qualified for dell credit, you probably also qualify for a Visa, Mastercard or (shameless plug for my current employer ) Amex card, and then you can make payments on it that way.