Simple plpgsql question

Hi,

I have, what I hope to be, a simple question about plpgsql.

I have a trigger on a table right now that updates a count everytime
that a new record is entered into a database (or removed).

What I'd also like to do is have it create a new row in a different
table using the automatically assigned id as a reference, but I'm
unsure of how to obtain the id of the newly created row in the first
table.

Example:
CREATE TABLE system_info (
id serial PRIMARY KEY,
name varchar(255),
value varchar(255)
);
INSERT INTO system_info (name,value) VALUES ('total_users','0');

CREATE TABLE master (
id serial PRIMARY KEY,
name varchar(32) NOT NULL CHECK ( name <> ''),
UNIQUE(name)
);

CREATE TABLE slave (
id serial PRIMARY KEY,
master_id integer REFERENCES master (id),
additional_info text
);

CREATE OR REPLACE FUNCTION update_users() RETURNS trigger AS $$
BEGIN
IF TG_OP = 'DELETE' THEN
UPDATE system_info SET value=(value::integer)-1 WHERE name =
'total_users'
RETURN OLD;
ELSEIF TG_OP = 'INSERT' THEN
UPDATE system_info SET value=(value::integer)+1 WHERE name =
'total_users';
INSERT INTO slave (master_id) VALUES (THIS IS WHAT I NEED TO KNOW);
RETURN NEW;
END IF;
RETURN NULL;
END;
$$ LANGUAGE plpgsql;

CREATE TRIGGER update_users AFTER INSERT OR DELETE ON master
FOR EACH ROW EXECUTE PROCEDURE update_users();

The part I need to know is the INSERT INTO statement in the procedure.

Any help would be great.

Thanks!