Windows Vista Beta 2 is currently available to MSDN and TechNet Subscribers. Unfortunately they did not make it publicly available like they did for Office 2007 Beta 2. However, Microsoft does say that in the next few weeks Vista will be released to people who are not subscribers:
Windows Vista Beta 2 is now available for IT professionals and developers with MSDN and TechNet subscriptions. In the coming weeks, Microsoft will start the Windows Vista Customer Preview Program (CPP) for developers and IT professionals who are not members of the subscription services.
I guess we will have to wait a little longer, but in the mean time you can play with Office 2007 Beta 2.
News Source: Windows Vista Homepage