automatic timestamp question

I have a table with a structure like:

CREATE TABLE xxx
(id int,
modified timestamp default current_timestamp,
created timestamp default current_timestamp,
something varchar(10));
somethingelse varchar(10));

What I want is for the modified field to automatically pop in the
current time whenever I update the record. The typical update would be
something like:

UPDATE xxx SET
something = "hello",
somethingelse = "goodbye" where id = 2;

What is the easiest, most generic way to do this?

In MySQL the first timestamp field (by default) automatically does this.

In PostgreSQL 7.0.3:
do I have to explicitly set the modified date?
do I have to create a stored procedure/trigger of some sort,?
or can I otherwise define behaviour that automatically happens
whenever the record is updated?

Thanks.

--
Richard Seymour : Anarchy Software, Inc.
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