Simple Text Field Encryption

I'm looking for a simple way to encrypt the contents of a text field in one
of my Postgres tables.  I'm not looking for anything that is bullet-proof --
just something that would mask the field's contents from a casual user
looking at the table via pgAdminIII or any other client application / query.

I'm hoping there is a built-in Postgres function that I could call from my
java web application to encrypt/mask a text string and then store the
encrypted value in the DB.  Thereafter, I would be able to query the
encrypted field, de-crypt back to the original value, etc.

Any suggestions would be appreciated.

BTW...I'm using Postgres v8.3 on Windows Server