cannot use $mysqli->set_charset (undefined method)

Hello, here are the versions I'm using : Apache/2.0.54 (Win32) PHP/5.1.0RC2-dev The mysqli client api version is : 5.0.13-rc (as written on my phpinfo output) I can instantiate mysqli with $mysqli = new mysqli("localhost", "root", "---", "mysql"); But I get an error when I try to set the charset with : $mysqli->set_charset("utf8"); The error I get is : Fatal error: Call to undefined method mysqli::set_charset() in .... I don't know what to do. I tried to reinstall php with the latest builds, did the same thing with mysql... Any idea ? Thank you Julien