need a password randomizer

does anyone know where i can find a php script that would automatically swap passwords after a specified timeframe? to be more specific, i have a client that wants to password protect a certain area on their site, but they want the password to change every so many hours. the pages they want to protect are for a sales presentation that will be used by their sales people to allow them to present their service online while on the phone. but, they don't want the clients to have access to it the next day or whenever. any help would be greatly appreciated.