You should research some other discussions here on Trulia for the specifics of rent to own contracts, but essentially, you are completing a lease agreeement in total, with a separate option agreement such that, within a specified period of time, you can purchase the property at a specified price. That right will most likely cost you an upfront fee of, maybe, $!0,000 and will be nonrefundable should you decide not to purchase the property during the option period. There's pro and cons to the rent to own agreement for both the buyer and seller. You will not be eligible for rights as a homeowner (the first time homebuyer tax credit, or other tax breaks) until you execute the purchase on the home.
But in any case, whatever home you're interested in, this question is best answered by the homeowner and a matter of negotiation.