Pre-foreclosure is a home that the bank has identified as one that will be foreclosed or one that the bank has just foreclosed on but has not listed for sale yet. The bank usually contacts a Real Estate agent and assigns a home they will have for sale ahead of it being listed for sale. The purpose is to have the agent prepare the pricing and recommend any repairs or other maintenance needs the home may have. The Banks will not sell directly to the someone without first listing it for sale and marketing it appropriately. Banks understand that they can get the best price for a home by exposing it in the MLS and using proper marketing techniques.
If the home is not yet foreclosed, but one the bank has identified as one they will most likely acquire through foreclosure, you would need to contact the current owner. They still hold title and the rights to sell the home until the bank does foreclose. In some cases these are listed for sale. In many cases these would be a short sale, where the owner owes the bank more than the home will sell for and therefore the bank will need to forgive part of the debt in order to complete this type of sale. If the home is not listed for sale, any REALTOR can find out who the owner is and approach them to see what the situation is and try to facilitate a deal.