とりあえず、ruby 1.1b6(98/01/23) [i386-cygwin32] では:

D:\Net\ruby\chk.rb>ruby -e "require 'GD'"
-e:1:in `require': No such file to load -- GD (LoadError)
        from -e:1

D:\Net\ruby\chk.rb>ruby -e "include GD"
-e:1: Uninitialized constant GD (NameError)

D:\Net\ruby\chk.rb>ruby -e "p GD"
-e:1: Uninitialized constant GD (NameError)

D:\Net\ruby\chk.rb>ruby -e "p Image"
-e:1: Uninitialized constant Image (NameError)

のようになります。

M.Kanemitsu