functions and triggers

I'm trying to build a trigger that will update a timestamp field in a table with
the current timestamp, and I just can't make it work.

The problemas are two:

1) when I try to create the trigger, it says that the function doesn't exist.
Why is this happening?
2) How does the trigger tell the function the row number identifier?

I'm really stuck with this.

Saludos... :-)

-- 
Porqué usar una base de datos relacional cualquiera,
si podés usar PostgreSQL?
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Martín Marqués                  |        mmarques@unl.edu.ar
Programador, Administrador, DBA |       Centro de Telematica                      Universidad Nacional
        del Litoral
 
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