Trying to give something back to the Community...
It seems that users of HP machines with AMD processors are encountering continual rebooting once they apply XP SP3. The problem is allegedly caused by the fact that HP originally loaded the Intel version of XP on these machines at the factory rather than the AMD version.
From what I can ascertain, after applying SP3 to one of the affected machines when you reboot the OS attempts to load a device driver for the Intel processor (which of course fails as the machine has an AMD processor), so it reboots, tries again, fails, reboots, you get the picture.
Both Microsoft and HP are working to resolve this but it seems Jesper Johansson, a former Microsoft security manager has beaten them both to it by releasing a free patch (unapproved of course by HP and Microsoft) at:
If you've got this issue and this patch helps let me know ;-)
It seems that users of HP machines with AMD processors are encountering continual rebooting once they