plpgsql question

Can I use table as a variable in a function ?
eg the following does what I need, (I have a trigger using it after an
insert on another table) but there will be a number of threads_whatever
tables and I thought it might be neater just using one function.
If it can be done - can I use a table as a variable in a sql function ?
Also bsides the docs and the pdf book - is there any other info around
on plpgsql ?

/* function to update threads table */
CREATE FUNCTION add_post_php() RETURNS OPAQUE AS '

BEGIN

IF (SELECT count(*) FROM threads_php WHERE thread_id = NEW.thread_id) <
1 THEN

INSERT INTO threads_php
(thread_id,date,user_name,last_post,last_user_name,posts,thread)
VALUES
(NEW.thread_id,NEW.date,NEW.user_name,NEW.date,NEW.user_name,count_posts_thread_php(NEW.thread_id),NEW.thread);

ELSE
UPDATE threads_php set last_post = New.date, last_user_name =
NEW.user_name, posts = count_posts_thread_php(NEW.thread_id) WHERE
thread_id = NEW.thread_id;
END IF;
RETURN NEW;
END;
' LANGUAGE 'plpgsql';