Additionally, you can download the whole package from Microsoft's Download Center. Remember, however, that at this time only the five language package is available (English (US), French, German, Japanese, or Spanish (Traditional)). The rest of the languages will release to manufacturing (RTM) in April.
Remember however that because of certain driver issues, not everyone will be able to see SP1 in Windows Update, at least until any problematic drivers on your system are updated. This was announced when Microsoft RTM'ed SP1.
Don't forget also that there are some prerequisite updates you need to install before installing SP1.
For those of us (like myself) curious as to exactly what the driver issues are, Microsoft went into detail in their blog post announcing the SP1 release today.
We spent the last couple of months looking closely at reports of driver problems on pre-release builds and, to be safe, we held the public availability until March.The list isn't long (fortunately), but even if you aren't offered the SP1 download via Windows Update, you can take a chance and download the whole package via the link I gave above.
We've completed our analysis and are happy to report that many of these issues were fixed between the release candidate (RC) and the final version. We identified a small number of device drivers that may be problematic after an update from Windows Vista to Windows Vista SP1. Check out the list here; we'll keep it updated with any additional drivers that we identify. As a result, we spent the past month or so working with our partners on driver updates for these issues. Of these drivers, most already have updated versions on Windows Update and are available for download now as optional updates. In a few weeks, we'll start to deliver these updated drivers to PCs automatically via Windows Update.
We're working with the providers of the remaining devices to get updated versions of the drivers to our customers as well. In the meantime, Windows Update will recognize PCs with drivers that may be problematic and postpone offering SP1 to those PCs until it has installed corrected drivers or other applicable updates. Either way, Windows Update works to detect whether or not your system is ready for SP1 and not offer it to you until the time is right.
For those of you who recall the problems some users had with one of the prerequisite updates (the Servicing Stack Update, KB937287), Microsoft believes they have pretty much resolved the issue:
By temporarily suspending automatic distribution, and making a small change on our Windows Update server, we believe we've largely eliminated this problem (and our support call volume reflects this). We did find one aspect of the problem that was exacerbated when the update was installed using automatic updates. For this issue, we're planning to release an additional update before we resume automatic distribution of the Servicing Stack Update.As I said previously, my advice is to back up your system before installing this update. If you don't have access to a backup or disk imaging program, I'd suggest you wait to see some feedback from end users before installing this. There's no reason to rush into an update this large.