Microsoft have made available build v6002-16497 of Service Pack 2 for both Windows Vista and Server 2008 to testers late last night. The bits show a compile date of October 17th and weigh in on average around the 3 Gigabyte mark.
Early reports show that the build has a smaller memory footprint, you can find more discussion here on our forums, we'll update this post when more information becomes available.
So far, x86 & x64 versions of English, German, Japanese, Spanish and French language have been made available for testing. If you were lucky enough to be selected, head on over to Microsoft Connect to pick up your flavor of the test build.
Link: Microsoft Connect (Registration required)