I don't think that Perl::Magick (Image::Magick perl modules) runs on Perl 5.6. I could be wrong though. But you should be able to install GD with the ppm command (If you're running ActiveState Perl) by typing : ppm install GD
I actually run ActiveState Perl 5.6 with Image::Magick. You have to compile it yourself, because there are no precomplied PPMs for it (at least not when I installed it), but it do work.