Column Specific Update Trigger Routine

I am trying to create a update trigger on a table that basically will only fire when a specific column is updated. I am using version 8.4.3.

My plan of attack was to always fire on any row update, and pass in the OLD and NEW column that I want to check.

CREATE TRIGGER check_lockout
AFTER UPDATE ON acct_table
FOR EACH ROW
EXECUTE PROCEDURE acct_unlock(OLD.userid,OLD.ownerid,OLD.password,NEW.password);

This fails with :

[postgres(at)linux1505 ~]$ cat check_lockout_trig.sql | psql testdb
ERROR: syntax error at or near "OLD"
LINE 4: EXECUTE PROCEDURE acct_unlock(OLD.userid,OLD.ownerid,OLD.password,NEW.password);

What am I doing wrong? Or is there a better way to go about this?