if you are doing a lease purchase you are agreeing to buy. here are the basics
1.You put down a non refundable deposit(usually 10%,but negotiable)
2.You agree to lease the house for a specified time(usually 2 yrs,but agina negotiable)at a price that is above market rent
3your deposit and extra funds are placed into an escrow account to build up yur down payment
4. At the end of the lease period yu go to a lender and get financing
5. if you do not go through with the purchase,you forfeit your escrow funds.. and the house can be put back on the market

if you are thinking about going this route,I urge you to work with a local agent who can look out for your best interests.

This would be tough...but if you find someone willing to do it aim to have 10% of your rent go towards the possible purchase on a price set today.