The Neowin website is reporting that SP2 invitation are going out. Some are already testing, others will get an opportunity in the next four weeks. SP2 is said to be delivered before Windows 7, so it should be in the next year or less. It will include Windows Search 4, support for VIA 64-bit CPU, and Bluetooth support.
See the original post at: Testers get invites to SP2 betas for Vista, Windows Server 2008 | All about Microsoft | ZDNet.com