Usually, in a pre-foreclosure, the bank has not taken over the propery yet. Once the lender takes over, then it's an REO (foreclosure sale), and the listing agent gets assigned and does pre-marketing duties prior to the sale. The bank usually wants the sale after the pre-marketing process.
If your intention is to buy before the bank takes over, then you need to contact the owner of the property and get into contract with him. If the property has a note above the market value, then you are in a short sale situation, which may require a professional's help.