modifying password in active directory

im using PHP4 for windows and im trying to create a user in an Active Directory (win2k). I succeeded in doing so but the only problem is changing the password. It always says "server unwilling to perform...". Can you help me solve this problem....
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HERE'S THE CODE which i got from other site:

$ldap = "somevalidconnection"

$newPassword = "somepassword";
$newPass = "";
// create the unicode password
$newPassword = """ . $newPassword . """;
$len = strlen($newPassword);
for ($i = 0; $i < $len; $i++)
$newPass .= "{$newPassword{$i}}00";
)
è$J·è$J·rd = $newPass;

$entry["unicodePwd"] = $newPassword;

$dn = "someDN";

ldap_mod_replace($ldap, $dn, $entry))
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