Once a house is purchased back by the bank after the foreclsoure auction, first they assign it to one of their local and approved Realtors. They look to see if teh house is vacant, if so they secure it, if not they start eviction. Once it is vacant, they clean the house, clear the deed and appraise the property. the house can be listed in as little as a day after the auction and usually up to 3 weeks after the house is deemed vacant and cleaned to sell. The listing agent usually posts a notice on the door so you can contact them direct before it is listed for the scoop.
Please see my blog for a full list of tips and advice on buying bank owned homes.