Beginning with PHP 4.2.0 these functions are enabled by default. For older versions you have to configure and compile PHP with --enable-ctype . You can disable ctype support with --disable-ctype .
The Windows version of PHP has built-in support for this extension. You do not need to load any additional extensions in order to use these functions.
Note: Builtin support for ctype is available with PHP 4.3.0.