Function To Log Changes

Hi All, I have been tinkering with a function to log the changes made on
any column through a function and trigger. However, I cant think of a way
to make this work through pl/pgsql. Any one have any ideas, or is it just
not possible?

SNIP
create or replace function logchange2() returns OPAQUE as '
DECLARE
columnname record;
c2 VARCHAR(64);

BEGIN

/* Cycle through the column names so we can find the changes being made */
FOR columnname IN SELECT attname FROM pg_attribute, pg_type
WHERE attnum > 0 AND typrelid=attrelid AND typname=''SOMETABLE'' LOOP

c2 := CAST(columnname.attname AS VARCHAR(64));
/* here lies the problem. How would I make plpgsql see OLD.columnname in
a dynamic fashion. I know this wont work whats below, but I am just
trying to express what I am trying to do */
IF ''OLD.'' || c2 != ''NEW.'' || c2 THEN
/* IF CHANGED DO SOMETHING */
RAISE NOTICE ''Update on column %'', c2;
END IF;

END LOOP;

return NULL;
END;
'
LANGUAGE plpgsql;

create trigger logchange2 AFTER UPDATE on TABLENAME FOR EACH ROW EXECUTE
PROCEDURE logchange2();