Make certain that your disk drive has the space required, at least 2GB for a
PC that is fully loaded with applications. This 2GB does not include the
recommended 15% free disk space requirement for Windows XP.
Install SP3 in 'Clean Boot' mode:
How to configure Windows XP to start in a "clean boot" state
http://support.microsoft.com/kb/310353
See the section titled: Manual steps to perform a clean boot in Windows XP,
skipping step 4.
Why clean boot:
A "Clean Boot" insures that only a minimal set of Windows Services and
applications are running. This means your Anti Virus software, third party
Firewall and other background applications will not be running; thereby
reducing the chances that installing SP3 will fail. Just remember to undo
the "Clean Boot" changes after installing SP3.
If I where to install SP3 I would choose to download the
file and not use Automatic Updates.
Where to download the SP3 installation file:
(File is large but will only install components that your PC requires)
http://www.microsoft.com/downloads/...a8-5e76-401f-be08-1e1555d4f3d4&DisplayLang=en
Steps to take before you install Windows XP Service Pack 3
Recommends steps to take before you install Windows XP Service Pack 3.
Also includes troubleshooting information.
http://support.microsoft.com/kb/950717/en-us