Service Pack 2 Release Candidate for Windows Vista and Windows Server 2008 are now available for download to TechNet and MSDN subscribers to test prior to final release.
SP2 for Windows Vista and Windows Server 2008 include updates that have been delivered since the release of SP1, as well as support for new types of hardware and emerging standards.
SP2 weighs in at a sizable 302MB for x86 systems and 508MB for 64-bit operating system versions of Windows Vista.
SP2 includes better application compatibility as well as some good hardware and software improvements for better performance. Windows Search 4.0 is now bundled with SP2. Check out the detailed list of notable changes in SP2.
SP2 is scheduled for release in the second quarter of 2009.
How this is different from SP3? I think SP3 would be more appreciable than this one.