http://homebuying.about.com/od/finan...7_leaseopt.htm
You can read about the differences here, although I will say that when we've structured the offers, the money that was non-refundable was allowed to be used as funds towards the downpayment when/if the option was exercised. The rent to own situation is something entirely different with generally no initial deposit made over the security deposits, but a portion of the rent goes towards the down payment.
As I said, it can't hurt to make the offer. And it would help to have yourself and Realtor figure out why it's adventageous to the sellers to take the offer and understand fully how it would work/be structured. Many agents do not think of doing lease-purchase-options, many don't think they come to fruition (and many don't) so they don't even bring it up with the sellers. I've had sellers tell me beforehand absolutely not but then when the offer actually came in, they sat down and thought long and hard about it. A couple of them changed their minds. And I have to say, neither of them actually closed...the market changed, buyer's circumstances changed, etc. but they kept the non-refundable deposit and security monies. These sellers may already be carrying two mortgages, similar to a situation that you would be in if you went for a straight purchase, and might be at the time when they need some relief that would come from the rent. You just never know until you make the offer. You are a stronger candidate, from my point of view, since you are not doing this because of poor credit, which is why most of these deals are done. You can offer a shorter term for the option...say 6 months vs 1 year. You are able to purchase outright, you just don't want to. So, your credit isn't an issue. That's a big plus.
If you consider purchasing this house and renting your own out to offset monthly payments, which pretty much makes the money outlays the same as doing it the way you are thinking, do yourself a big favor and make sure you get people in there that are agreeable to having the house shown while they are living there and do a short term lease if not month to month. It's difficult to sell a house with a tenant in it.
I don't know how much money you are working with...is the seller able to hold some paper? If so, you may be able to work a deal where you 'purchase' now, pay their mortgage payments, they forgo payments on any loan they are making to you until the end of the term...say a year with interest being tacked on to the balloon payment. That might buy you the time to sell your house, get them out of their situation.