This is supposed to be appearing in Windows Update today, so I would wait for it to show up there. But if you’ve got the guts, you can download it here right now.
An overview as to what this covers can be downloaded here.
If I were you, I’d wait for braver souls to download it and find all of the problems before you jump in. But if you must jump in now, have a complete backup of your system just in case things go really south.
I’ll try this later tonight on one of my VMs and let you know what I think of it.
Update: Just tried Windows Update. No sign of it.
Update #2: This was just posted to news.com. Apparently it doesn’t play nice with another Microsoft prouct called The article also gives details as to why it’s not available through Windows Update. I’d say avoid it for now unless you have a current backup.
Update #3: Apparently Vista SP1 has the same problem. According to this post, it has been halted as well.