This is available for direct download from Apple's Web site, as well as from the Software Updates control in Mac OS X. It's available in multiple language versions and appeared on Apple's site late yesterday.
It improves support for installing software updates and, Apple warns, "is required for any future Mac OS X updates". The company has not disclosed if the release was thought necessary to prevent the kind of data-loss problems encountered by some X-wielding iTunes users earlier this month. This was attributed to a corrupted installation file.
Apple has also released its Detailed instructions for the management of songs and playlists on iPod, its £349 MP3 player, have also been released.
Also available for download is QuickTime Streaming Server 4 Public Seed. This is a trial, pre-release, time-limited version of QuickTime Streaming Server, meant for evaluation and development only. Apple warns that it should not be used in a commercial operating environment, or used with important data. The software expires on March 15, 2002.