Just minutes ago, Microsoft released yet another refresh of Windows Vista to it's beta testers via Microsoft Connect.
Buid 5728 is available in both X86, which is about 2,622MB (2.6GB) and X64 which is just over 3,620MB (3.2GB). The download is available in English, German and Japanese.
Also available, is build 5728 of Windows Longhorn Server which is also available in both X86 and X64.
This is a pre RTM build, and is not the final build which will be released to testers.