There is a very common misconception out there that Group Policy Preferences can only be created, managed and applied to your Windows machines if you are running your domain controllers with Windows Server 2008 or later. This is so NOT true.
What you have to do if you are stuck on domain controllers running Windows Server 2003 is to install the Remote Server Administration Tools on a Windows 7 (or Vista) client machine, add the feature Group Policy Management and then create a GPO in the domain and edit it, configuring the Group Policy Preferences of your choice. Voilà!
I do not know where this myth is coming from actually but the fact that GPO Preferences were introduced in Windows Server 2008 is the major reason I would assume.