Umm.... what PHP installer are you talking about? If it's the one from php.net, there are no external extensions included. As GD is an extension, it falls under this category. Does PHP work otherwise (excluding GD I mean)? If so, grab the zip off of php.net, extract it, move the extensions to whatever folder the extension_dir is set to in php.ini and uncomment the load GD line. Restart IIS and you should be good to go. Let me know if it doesn't work....
-geoff