reversion? Recursion question

Hello,
For lack of a better title, I need to a reverse recursion. Where I have
the parent ID, but then I need to find all it's children, grandchildren,
great-grandchildern, etc for the parent-id. I guess this would be like a
directory and all its sub-directories.

I modified a normal recursive function I got from the cookbook , but it's
impossible for me to decipher where the top level begins and the children
end.
Could someone point me in the right direction to clean this up? I can
provide sample data if needed.

TIA
Patrick Hatcher

-Table
CREATE TABLE mdc_category (
keyp_category int4 NOT NULL,
category_name varchar(255),
parent_keypcategoryid int4,
CONSTRAINT xpkmdc_category UNIQUE (keyp_category)
)

CREATE FUNCTION category_descriptiontest(int4) RETURNS varchar AS '
DECLARE v_category_id ALIAS FOR $1;
DECLARE tmp_record RECORD;
DECLARE tmp_id VARCHAR;
DECLARE tmp_code VARCHAR;
DECLARE keycheck INT4;
BEGIN
tmp_code:='''';
FOR tmp_record IN SELECT keyp_category,category_name,parent_keypcategoryid
from mdc_category where parent_keypcategoryid = v_category_id LOOP

IF tmp_record.parent_keypcategoryid=0 THEN
RETURN tmp_record.keyp_category;
END IF;
tmp_id:=category_descriptiontest(tmp_record.keyp_category);
IF tmp_record.keyp_category<>0 THEN
tmp_code:= tmp_code || ''
-'' || tmp_id::varchar || tmp_record.keyp_category::varchar || '' -
'';

/*
tmp_code:= tmp_code || '''' || tmp_id::varchar || ''
-'' || tmp_record.keyp_category::varchar;
*/
END IF;

END LOOP;

RETURN tmp_code;
END; ' LANGUAGE 'plpgsql';