在php.ini里面，extension=php_mcrypt.dll，去掉前面的;，重启apache，报错：
PHP Warning: PHP Startup: Unable to load dynamic library 'd:/AppServ\\php5\\ext\\php_mcrypt.dll' - The specified module could not be found.\r\n in Unknown on line 0
[Sat Sep 26 13:13:18 2009] [notice] Apache/2.2.8 (Win32) PHP/5.2.6 configured -- resuming normal operations
[Sat Sep 26 13:13:18 2009] [notice] Server built: Jan 18 2008 00:37:19
[Sat Sep 26 13:13:18 2009] [notice] Parent: Created child process 2612
这个提示不是说找不到php_mcrypt.dll，而是不能加载php_mcrypt.dll。
解决方法：
去下载libmcrypt.dll，然后放在apache的bin目录下。就可以了。
下载地址：http://files.edin.dk/php/win32/mcrypt/
转自http://blog.chinaunix.net/u/10668/showart_2060534.html