Codice per http://lloc.it/i-presupposti-minimi-di-un-sistema.html

register_activation_hook.php

<?php

define( 'MYPLUGIN_MIN_PHP', '5.2' );
define( 'MYPLUGIN_MIN_WP', '2.8' );

function myplugin_activate () {
	$error      = '';
	$phpversion = phpversion();
	if ( version_compare( MYPLUGIN_MIN_PHP, $phpversion, '>' ) )
		$error .= sprintf( "Minimum PHP version required is %s, not %s.\n", MYPLUGIN_MIN_PHP, $phpversion );
	$wpversion = get_bloginfo( 'version' );
	if ( version_compare( MYPLUGIN_MIN_WP, $wpversion, '>' ) )
		$error .= sprintf( "Minimum WP version required is %s, not %s.\n", MYPLUGIN_MIN_WP, $wpversion );
	if ( !$error ) return;
	deactivate_plugins( __FILE__ );
	die( $error );
}
register_activation_hook( __FILE__, 'myplugin_activate' );