Put that in a file and open it in your browser. Check the first table that comes up for "Configure Command" and see if it says --with-gd anywhere in that string (most likely --with-gd=shared). You can also scroll down and look for the 'gd' configuration table (should be after ftp and before hash), and check that all the options are enabled and not disabled for some reason.
-m

edit: To make sure the dll is there, it should be in your path\to\PHP\ext\ folder, named php_gd2.dll