OK, I did it at last.
For anyone else wanting to do this you need the php_gd2.dll. Place this in whichever directory you've set as your include path. I also put it in c:/PHP and the windows file for good measure.
Then just uncomment the
extension=php_gd.dll
line in php.ini and of course change it to:
extension=php_gd2.dll
Good Luck