From LedHed's Wiki
Service Pack Command Line Switches
/Z Suppress Reboot /M Unattended Install (Win2k) /U Unattended Install (WinXP) /F Force Programs to close at Shutdown /N Do not Backup Files /Q Quiet, No user intervention required /X Extracts files to a specified folder
Example:
XP-SP3.exe /Z /U
Unattended install of XP-SP3 suppressing the reboot.
XP-SP3.exe /X C:\Temp\XPSP3
Extracts the Service Pack Files to the destination directory C:\Temp\XPSP3