Contributed By: Cliff Hobbs [MVP SMS]
Microsoft have released the following information that should help you workout how to deploy Windows XP SP2 using SUS:

Deploying Windows XP Service Pack 2 using Software Update Services
This page walks you through the process of deploying XP SP2 using SUS:

http://www.microsoft.com/technet/prodtechnol/winxppro/deploy/xpsp2sus.mspx

FAQ – Deploying Windows XP Service Pack 2 using Software Update Services (SUS)
As it's name suggests this page contains various FAQ relating to deploying XP SP2 using SUS:

http://www.microsoft.com/technet/prodtechnol/winxppro/deploy/xpsusfaq.mspx