How can I load load Additional extensions ?

My OS is Winxp . My web server is apache 2 which is installed as a NT service . My php version is 4.32 , and I extracted it into "c:\php" . I run php as a apache module . I want to load Additional extensions .They are php_mbstring.dll, php_xslt.dll and php_domxml.dll . I have made changes to php.ini as follow. extension_dir = "c:\php\extensions" extension=php_mbstring.dll extension=php_xslt.dll extension=php_domxml.dll then I restarted apache2 . but it told me that the modules could not be located . what was wrong ? thanks for any useful words .