If you're talking about the SAME property, it's called a lease-option. You're leasing the property with the right to purchase it. Or you could do a lease-purchase, in which you lease the property but you've committed to buying it.
If you're talking about renting one property and buying another, that's possible, too. One hurdle is qualifying for the purchase since you'll then have two monthly payments--one for the rent and the other for the purchase.
Hope that helps.