Common code base for Vista, Longhorn Server CNET News.com: "'The plan is unlike (Windows) XP and (Windows Server) 2003, where we had separate code bases. We'll have one code base,' Muglia said. 'That will all converge next fall, roughly...when Longhorn Server ships.'
As the Vista team patches bugs in the desktop operating system, those changes will be folded into the Server code. Meanwhile, the changes to the Server code will be added back into Vista in a service pack for the desktop operating system, currently slated for delivery next fall. "