SP1 for Vista will not likely be similar as SP1 for XP.
Microsoft has said that they are going to be pushing out fixes and updates
via Windows Update to a much larger extent than they do in Windows XP.
You may well get the equivalent of SP1 in drips and drabs over the course of
6-12 months.
I don't see the massive service packs that were the norm with Windows XP,
under Vista.
Then again, something major may materialize that will change this scenario.
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Regards,
Richard Urban MVP
Microsoft Windows Shell/User