Both of the previous answers had some very helpful information. The most helpful information is that EVERYTHING IS NEGOTIABLE!!! Personally, I haven't dealt with FHA for probably about 10 years now and I know that even in the past 6 months ALL financing has changed a lot. But based on my years as a consumer buying, selling and financing my homes and my experience with FHA, lease/purchase or rent-to-own might require the same level of negotiating (being just as easy or just as difficult) as buying via FHA.
My experience has been, when you buy a house via FHA, the homeowner MIGHT have to spend a good chunk of money fixing the house up to meet FHA standards. This becomes cash out of the seller's pocket with the chance that the sale won't close. Granted, disclosure laws and home inspections have changed a lot in the past decade so this situation occurs more frequently than it used to even with conventional loans. However, because this is a buyer's market, if you are the only buyer a seller has received an offer from and they really need to sell the home, they will be willing to make the investment to make the deal happen.
On the flip side, let's say a seller has a home in need of repairs but she doesn't have the money to make improvements. Because the home has orange shag carpet and 70-year-old, dirty, lace curtains, the home hasn't sold for over the past year plus that it has been on the market. The homeowner had to move out into a nursing home or with family. She can't even afford to pay her most recent $3000 tax bill and her monthly $500 mortgage payments. The house is not in foreclosure (yet) and is listed for sale at a bargain price of $200,000 - which would be $6000 down and monthly payments of about $1750.
You, through a Realtor qualified in negotiations and a Real Estate attorney, offer to buy the house for $200,000 in one year, put down a non-refundable $3000 deposit so that she can pay her tax bill and you pay $1000 a month so that she can pay the mortgage and the next tax bill. You agree that you will do $750 per month worth of work to improve the home that will go toward prepayment of your down payment next year. By the time you close, you will have the original $3000 down, another $9000 in credit and you should be saving the other $3000 along with $500/month. This will now give you 10% down and a home that is worth more than $200,000 because you have made improvements.
The first month, you do 10 hours of manual labor per week including tearing up the carpet. The second month you have to spend real money and pay $350 for a dumpster for the carpet, rent the sanding equipment, and other supplies and also do 5 hours of labor per week. As you can see, this is very doable and is win-win for everyone.
The moral of the story is, look for homes regardless of whether the seller will accept lease or options or FHA or even owner financing. And then make an offer that works for everyone.
P.S. Some of the above information (mostly numbers) is based on an actual home for sale in Oak Park, other information (mostly situational) is fictional (although highly likely).
Here's a link to a recent posting of mine with a dozen or more ways to find lease-option and rent-to-own properties: http://www.trulia.com/voices/Home_Buying/How_can_I_find_opti
Finally, in reference to another posting here, the time frame for a rent-to-own is negotiable. For a number of reasons, it should be for at least a year. I know of rent-to-owns that have a time frame of 2 years, 3 years, or even longer.
Hope that helps.