'now - 4 hours ago' ?

I'm still learning SQL. :-)

Now I have upgraded my PostgreSQL database to v6.3.2, and have the
following table.

  CREATE TABLE testdate(
       received timestamp DEFAULT CURRENT_DATE,
       info text NOT NULL
       );

I want to select the info received (inserted) more then 4 hours ago.
How do I specify that in SQL?  Is timestamp the best datatype for this
kind of query?  Which date-types exists in PostgreSQL, and what is the
difference between them.  I'll be very happy to get pointers to good
intros. :-)

I'm not on this list, so please send copies to me.
--
##>  Petter Reinholdtsen <##    | pere@td.org.uit.no
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