Those are two different (and mutually exclusive) things: foreclosures and rent-to-own. Foreclosures are owned by banks. They want to sell, not rent or engage in lease-options. On the other hand, you may find some rent-to-owns or lease-options among financially stable sellers. (And you definitely want someone who's financially stable. If the seller goes bankrupt or loses the house to foreclosure, your lease-option becomes worthless.)
Here's a link to a blog I wrote on how to find rent-to-own properties: http://bit.ly/findaleaseoption
Hope that helps.