PHP 4 can not connect to mysql server with error "Client does not support authentication protocol"

MySQL 4.1+ uses an authentication protocol based on a password hashing algorithm that is incompatible with that used by older (pre-4.1) clients. MySQL extension for PHP4 was compiled with old (pre-4.1) client library.

When you connect to server. It will shows error

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

To solve this problem, you should use one of the following approaches:
1. reset password to old style password

SET PASSWORD FOR 'some_user'@'some_host' = OLD_PASSWORD('newpwd');

For PHP mysql_connect command, you must specify parameters following

mysql_connect($server,$user,$pass,false,0);

2.Tell the server to use the older password hashing algorithm:
add this line to mysql configuration (my.ini/my.cnf)

[mysqld]
.
.
old-passwords = 1
.
.
[client]
.
.
old-passwords = 1
.
.

then restart service and reset password using command

SET PASSWORD FOR 'some_user'@'some_host' = PASSWORD('newpwd');