How to track exceptions in PL/pgSQL

Hello,

I would like to track (timestamp and error number) in the database or
in text files the exceptions that occur in my PL/pgSQL functions.

1. How can I retrieve the SQLCODE in a 8.0.3 PG server ?
2. How can I trace the exception in a table although an implicit
rollback is done when a exception occurs (the trace will be rollbacked
too) ?

Thanx