Microsoft is going to release several new security content on April 28th; among other is an update, showing that Vista SP2 is expected early next month: Update for Windows Server 2008 and Windows Vista (KB955430)

Deployment: Important/Automatic Updates, WSUS, and Catalog
Classification: High Priority, Non-Security
Target platforms: Windows Server 2008 and Windows Vista
Approximate file sizes:
-Windows Server 2008 for IA-64 update: ~ 14268KB
-Windows Server 2008/Windows Vista update: ~ 4287KB
-Windows Server 2008 x64/Windows Vista x64 update: ~ 10148KB