Credit score is not the only measure of one's ability to purchase a home. I believe, most lenders will consider a FICO score of 550 or lower, to be outside of the acceptable range for most of their programs.
However, home purchasing is not always limited by a low credit score and there are numerous other options for purchasing a home. I am guessing you would not have asked this question if you had the cash on hand for an outright purchase, but cash is an option that does not rely on credit scores. Other options may include private held mortgages, owner carry loans, or other more complex transactions such as a lease purchase which will require an attorney's involvement.
For a better answer to your question about credit scores however, I would suggest checking with a reputable local lender. Often times your trusted Real Estate agent can provide you with contacts for those individuals if you do not have one.
In instances where you are concerned about your credit score and looking for ways to "re-score" or follow a rapid recovery program, the best lenders will also have programs or be able to assist you directly in the necessary steps toward repairing or improving your credit situation. Be cautious in this area, there are scams out there that will promise you results for an exorbitant fee that gets you little or no real results. Quality mortgage providers often will counsel and guide you on this process for very little or no out of pocket expense.