One idea would be to manually create a system restore point just prior to seeing SP3 installed. If you should run into any problems you can use that to bring the system back.
The other option is uninstalling the new service pack by the add/remove and having the "show all updates" option checked off. The service pack should however go on without problem and contains some 1,000+ fixes MS finally got around to releasing for XP there.
Any news about AMD compatibility?