If you're interested in doing a lease-purchase, the first thing you need to do is find an agent that is experienced in them. Otherwise, you'll get responses like the one before.
If you haven't yet, research the term lease-purchase, lease-option and educate yourself on it a bit.
In a lease option deal, as the buyer, you'll usually be required to put down a good-sized option fee. Make sure that you are prepared for that. When lease options "don't work out" it is rarely the seller is unable to close the deal because the value has dropped too much (there's a fix for that as well, if it would happen), but rather because the tenant/buyer is a) decided not to buy (ie, it didn't work out for the seller) or b) the tenant/buyer did not work enough on their credit/financial situation to be in a position to buy.
A lease option is a lease with the option (but not the obligation to buy). As a tenant/buyer you don't have to purchase if you decide you don't want to buy anymore.
The real key is understanding where you stand financially and credit-wise. You want to make sure that you are in a position to buy it when the time comes if you want to buy it.