Peng's Mac4Lin GDM Login Screen
Source (required if based on other people's work):
Based on infrareddude's Mac4Lin Login Theme (with both his knowledge and his permission), this version proudly displays that it's for Mac4Lin rather than OSX Leopard. Includes the new Mac4Lin "logo" that I created for the Mac4Lin Transformation Pack version 0.4 (http://sourceforge.net/projects/mac4lin).
You'll need the Gnome system login tools or the equivalent to change your login screen.