On pre-foreclosures, they are typically owned by the bank. There is no reason or incentive for them to want to do a rent to own scenario. What would they have to gain? Ideally, they would like it vacant, so it can be shown by an agent at any time.
If the home is still owned by the homeowner, they have lost control of the situation, and you will not be dealing with them when it comes time to buy. Generally speaking, rent to own is not a good deal. You must be careful how you structure it if you decide to do something like this. If you decide to go ahead with it, be sure to have a real estate attorney review the contract. They are often written in favor of the seller.