PHP and MYSQL record locking

We have a multi-user database we use for telemarketing. It is used across the internet. All the pages are PHP, I am trying to lock or keep other users from accessing the same record, so that they do not call the same lead. For example, the user selects a zip code to work from and then a lead pops up, once the lead has popped up on the callers screen, I don t want that same lead to pop up on anyone else's screen. So I am not sure if I need to lock the row, or if there is a better way of doing it, since the web browser is stateless. Please any help you can provide would be great, because I have searched the net and haven t found much information. Thank you. -Jason