Microsoft previously announced that Windows Vista SP1 would arrive together with Longhorn Server in the second half of this year.
But in recent months, other Microsoft officials have tried to muddy the SP1 waters, claiming Microsoft had no timetable for Vista's first service pack. Such a claim might even be believable, given how long (2008!) Microsoft is delaying delivery of Service Pack 3 for Windows XP.
Why the secrecy, Microsoft? Customers, especially many corporate ones, are still using SP1 as a marker for when they'll consider deploying a new software release. By refusing to provide an SP1 ship target, you've been creating more FUD.