Several PRECAUTIONS should be done PRIOR to upGRADING ( from SP2 to SP3, for

example ) an Operating System. which I feel should include the following :

1) Get the latest RELIABLE Info on possible problems; I trust the FREE "Windows Secrets"

& "Don't let XP3 hose your system" from http://WindowsSecrets.com/080911 is very good .

2) Make reasonable sure the computer is Malware-free ; practically speaking, nowadays

that means running the "Full Scan" of the FREE Ver of "SUPERAntiSpyware" from

http://www.superantispyware.com/ AND the "Free" Version of "Malwarebytes' Anti-Malware

from http://www.malwarebytes.org/mbam.php .

3) Get the latest PC Manufacturer "Driver" updates , IF there are any .

4) Make a "System Restore" Point, to go back to, IF the Installation is NOT successful .

Refer to the excellent Guide at http://www.bleepingcomputer.com/tutorials/tutorial56.html

If I remember correctly that SP3 actually improve bootup time and system performance.

It will do these changes to your computer without your consent-

Will change the cursor back to default

Will undo a fix with the background intelligent transfer service. (want more info?)

Will re-enable the default sounds

Will nuke any custom theme you had set up

If you don't need an upgrade, don't upgrade. If it aint broke, don't fix it. You could send your stable running PC into a series of blue screen of deaths after the SP3 install.