> Does anyone know wwhere the might be a useful shopping cart system for
> pgsql+php3,
In Answer to your question: try PHPLIB (http://phplib.shonline.de/)
it's not Postgres specific but it can use Postgres.
A couple of thoughts:
1. Why don't you just write one? PHP's learning curve isn't that steep
and it would be a good exercise.
2. You would find that the PHP list is more responsive for apps such as
the one you are requesting.
3. Did you know that there's a PHP&PGSQL mailing list?
Hope this helps,
DEJ