Microsoft, it appears, has just released Windows XP Service Pack 3.  For the most part, it is a bundle of all the updates since Service Pack 2, but there are some key differences.  First, the big gotcha:

If you are an IE 6 user, SP3 will simply updated your IE 6 installation.  You will continue to be able to upgrade to IE 7 as an option.

If you are an IE 7 user, it will update your IE 7 installation.  HOWEVER, you will NOT be able to go back to IE 6 after applying this service back.

If you are an IE 8 (beta) user, you will need to uninstall IE 8, apply the service pack, and then reinstall IE 8.

This link has a list of all the Knowledge Base articles that this service pack addresses.  Some of the bigger notes is that it does retrofit some of the Vista functionality into XP, namely in the area of Network Access Protection, Black Hole Router Detection, enhanced security for administrator and service policy entries (basically some better default settings) and a kernel mode crypto driver.  Additionally, some of the "optional" updates released since SP2 will be installed with SP3 (MMC 3.0, MXSXML6, WPA2 support, etc).

The good news is that TechNet provides installation media that can be used to slipstream install the service pack so workstations can be updated off the net.

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John Bambenek / bambenek \at\ gmail /dot/ com