Neil Hutson announced on his blog that he and his team have created an automated tool called the "Works With Windows Server 2008" tool.
The tool performs automated tests for you and provides a report on success. That report can then be sent to Microsoft if you want to be part of the Windows Server 2008 catalog.
The tool is in it first beta form now and will be in RTM in the next month or so. To download it, please go to the following link.
Microsoft, Works With Windows Server 2008, Tools, Software, Announcement