Encryption in the tables of a Postgres 7.3.2 database

Hi,

I've a Postgres DB release 7.3.2 and some developed C++ and PHP code
so as to communicate with it.

Currently, the data I've in the different tables is stored with no
encription at all, and I was wondering if there would be an easy way
to get it encrypted without major changes in the already developed C++/
PHP code.

I mean, I want to replace the non-encrypted database with an encrypted
version of it without C++/PHP programmes noticing it.

Has anyone any suggestion about the easiest way to do it?

Thanks.