mailing address regexp

I ask this here because PHP developers are notoriously famous for knowing RegExp... the project in question isn't for PHP, but perhaps you can still be a bit of a help? I need help in formulating a RegExp that'll detect PO Box addresses... the problem is the many different ways a PO Box can be expressed.. PO Box PO P.O. Box P O P O Box PMB etc... Anyone care to help out a bit? I would greatly apperciate it!!!!