Regular expression help

[rjette]

I am attempting to create a regular expression to give a negative score for 
purchase orders. I need to match the following:
PO
PO:
PO#
P.O.
P.O. #
PO #

I have not been able to get this to work correctly. I have the following:

/\bP\.?O\.?[:#]? [#]?/i

Any ideas?

Thanks in advance.

Ray