what you are describing is a rent with option.
A LEASE/PURCHASE actually has a purchase contract on the property (it took me 2 years to close one of these for someone with crappy credit - and headaches along the way that were close to igraine-level (couldn't understand that he needed to pay his rent 'on time' and was 90days overdue twice in 15 months); At one year from the original signing of paperwork - he didn't have the money to close (had to extend another year). - he got behind in rent twice that year.
I actually inherited this case as a manager when the agent left the business... it should never have been written in the first place is all I will say. BTW - he got foreclosed on seven months after purchase.
Clean up your credit first - there will be house at the end of this year and into 2009 if not 2010...
Will I do another one - yes - but I will have an assumption package to start (agent never ordered one - so no way of knowing how much the buyer had to pay) or a payoff on the house and require verification from the buyer as to assets - and a hefty deposit (held in escrow) - this would be 'my best advice' to my client.