automatic pgp decryption for specific mailbox??

Could someone tell me how to automatically perform a pgp decryption for mail
delivered to a particular mailbox and then pipe that decrypted message
through a program that performs an action on that STDIN.

I have got it working fine for a non-encrypted message, but, as soon as I
tried to accomoddate pgp encryption it broke.

Here is what I was using to get a non-encrypted message processed (this
works).

:0
| /usr/local/bin/test.pl

Here is what I tried to perfrom and additional step of decrypting the
message before piping it to my program (this does not work).

:0
| pgp -m | /usr/local/bin/test.pl

I also tried
:0
| pgp -o - | /usr/local/bin/test.pl

Any help would be appreciated.

Thanks,

Bil