MySQL 5.0 uses an authentication protocol based on a password hashing algorithm that is incompatible with that used by older (pre-4.1) clients. If you upgrade the server from 4.0, attempts to connect to it with an older client may fail with the following message:

Client does not support authentication protocol requested
by server; consider upgrading MySQL client

Reset the password to pre-4.1 style for each user that needs to use a pre-4.1 client program. This can be done using the SET PASSWORD statement and the OLD_PASSWORD() function:
mysql> SET PASSWORD FOR  'some_user'@'some_host' = OLD_PASSWORD('newpwd');

Alternatively, use UPDATE and FLUSH PRIVILEGES:
mysql> UPDATE mysql.user SET Password = OLD_PASSWORD('newpwd')    -> WHERE Host = 'some_host' AND User = 'some_user';mysql> FLUSH PRIVILEGES;

地址：http://dev.mysql.com/doc/refman/5.0/en/old-client.html