You can also buy a house regardless of credit if there's owner financing and the owner agrees to it.
One point a lot of people here on Trulia will raise is: What is your credit? You should go to a lender or mortgage broker and really determine what your credit is.
And that's good advice. There are different criteria for different types of loans. "Poor credit" means different things to different people.
However, assuming your credit isn't good enough to qualify for a traditional loan (that appeared to be the basis for your question), then you have to use non-traditional or creative financing. And that includes lease-option/rent-to-own homes. However, understand that the owner still cares about your credit. He/she just doesn't have the same standards as a traditional lender might.
Understand, too, that at some point you'll have to go out and get conventional financing. Many/most rent-to-own homes are for periods of 1-5 years . . . more typically 2-3 years. After that point, the owner will want his/her money. That 2-3 year time frame gives you enough time to clean up your credit, build up some savings, and position yourself to buy. Then you go out and get a mortgage for the remainder owed, and the seller receives his full payment.
Hope that helps.