Well auto-update is anyway the first thing that is advised to be turned off after first startup of Windows XP. Updating recommended here or there, you might not want to sent Microsoft your personal data which is happening during auto-update, and if you're so desperate for those updates, you can always do it manually.
I never installed any updates for Windows XP Pro SP2, nor did I install the Service Pack 3, and I never needed any, either. But that's my personal experience since I tend to hold my systems in firm control and know where's what, it might be different for others and actually provide some benefit to them, especially with the newer hardware.
But so or so, if you remember how the system requirements doubled from SP1 to SP2 it might be woth considering if you need this SP3 at all. If the hardware already runs without problems with SP2, why would SP3 be necessary?
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