Currently Vista SP2 is rumored to be scheduled for RTM (release to manufacturing) in April. The blog post did confirm a 1H 2009 release date.
The post says that starting on Dec. 4th, everyone (meaning the general public, too) will be able to download the current beta build of Windows Vista SP2. You'll be able to download the beta here, at TechNet.
Just to repeat, yes, even non-subscribers will be able to access the beta. MSDN and TechNet subscribers already have access.
Microsoft gives the standard warning about beta products:
The CPP ( Customer Preview Program) is intended for technology enthusiasts, developers, and IT Pros who would like to test Service Pack 2 in their environments and with their applications prior to final release. For most customers, our best advice would be to wait until the final release prior to installing this service pack.Techies who read this blog will probably not be too concerned, but remember my advice is always to wait a day or two (not that I follow that advice) before upgrading systems, gaming consoles, etc. etc. with new software / firmware. Wait for it to sort out before you try (or at least backup your system). There are many examples of early adopters getting the "shaft" by a bug.