I do not want Service Pack 2 installed now but I want to leave Automatic Update enabled

If Automatic Update is enabled for a sufficient amount of time, an icon will appear in the Notification Area by the clock.
Hover the mouse over the icon and you will see information about the update.

1. Double-click the icon or the pop-up.
2. Click "Custom" to display available updates.
3. Uncheck the box next to Service Pack 2, then press the "CLOSE" button
4. Check the box by "Don't notify me about these updates again".

This procedure allows you to keep Automatic Updates enabled and at the same time prevent the installation of Service Pack 2.
You should periodically verify the reasons for not installing Service Pack-2 are still valid and consider installing if circumstances change sufficiently.

WARNING: You should not do this unless you have a compelling reason for not installing SP-2.
Service Pack 2 has many improvements not just in performance, but also security.
See this link for more information:
Windows XP Service Pack 2
Follow the Service Pack Installation Checklist to help be sure your computer is ready for Service Pack 2.

Service Pack 2 is important, install it when possible