Syntax:
OLD_PASSWORD(str)

OLD_PASSWORD() was added to MySQL when the implementation of PASSWORD()
was changed to improve security. OLD_PASSWORD() returns the value of
the old (pre-4.1) implementation of PASSWORD() as a binary string, and
is intended to permit you to reset passwords for any pre-4.1 clients
that need to connect to your version 5.1 MySQL server without locking
them out. See
http://dev.mysql.com/doc/refman/5.1/en/password-hashing.html.

URL: http://dev.mysql.com/doc/refman/5.1/en/encryption-functions.html

