Hello,
I have a solution that actually works fine.
Firts i have unzipped this file for a french XP SP3 :
WindowsXP-KB936929-SP3-x86-FRA.exe
In a batch i wrote this line (according that %source% is the root folder where the file has been unzipped) :
start %source%\WindowsXP-KB936929-SP3-x86-FRA\i386\update\update.exe /quiet
At last i execute a job in Altiris DS 6.9 :
And it installs silently without any UI.
It does reboot after installation so globally we schedule this job when nobody is logged on the PC.
Hope it could help you!
Best regards.