http://www.microsoft.com/downloads/d...displaylang=en
Has a brief description and links to more detailed descriptions of what SP3 includes.
http://download.microsoft.com/downlo...20Pack%203.pdf
is the PDF overview
It is well worth reading the whole thing but here are some excerpts
"Windows® XP Service Pack 3 (SP3) includes all previously released updates for the operating system,
and a small number of new updates to ensure that Windows XP customers have the latest updates for
their system. Windows XP SP3 will not significantly change the Windows XP experience"
Windows XP SP3 does not include Windows Internet Explorer 7,
although Windows XP SP3 does include updates to both Internet Explorer 6 and Internet Explorer 7, and it
will update whichever version is installed on the computer.
SP3 does include Network Access Protection (NAP) to help organizations that
use Windows XP to take advantage of new features in the Windows Server® 2008 operating system.
Other new features it adds are
"Black Hole" Router Detection ((detecting routers that are silently discarding packets)
CredSSP is a new Security Service Provider (SSP) that is available in Windows XP SP3 via Security Service Provider Interface (SSPI).
Descriptive Security Options User Interface
Enhanced security for Administrator and Service policy entries
Microsoft Cryptographic Module
Enhancements to Windows Product Activation / Window Genuine Advantage which allow upgrade and download of additional components without requiring you to enter your product key as would otherwise be necessary.
==================================================================
Essentially there are several major reasons to install this update.
One is that as with XP with no service packs, and XP SP1 ; SP2 will eventually no longer be supported through windows update or direct product support.
Secondly it ensures that you have all the security updates which are critical to a safe and stable machine.
Yes, there are a few reasons not to install; such as if you have one of the HP machines with AMD processors which had an Intel based image installed and crash when the update is installed. Or if you have a malware infestatation.
But if your computer is otherwise up to date, it is well worth installing.
http://support.microsoft.com/kb/936929
Contains the release notes