WSUS SP1 is right around the corner, and so is the ability to have your Vista Beta 2+ clients sync updates from WSUS. Check out this link for information on how to point your WSUS SP1 server to an alternate update stream so you get Vista updates.
Basically it breaks down like this…
At the command prompt type:
cscript.exe "%programfiles%\update services\tools\ToggleMUUrl.vbs" beta
This enables your WSUS box to sync with a special version of Microsoft Updates that includes Vista patches. To revert back to the normal update stream, type the following command:
cscript.exe "%programfiles%\update services\tools\ToggleMUUrl.vbs"
Stay tuned to the WSUS Team Blog and this site for an announcement on SP1 availability.