I had read an article about this, and still I had this problem when I installed SP3 on one of the office computers. Windows Automatic Update offered to install Service Pack 3, so I accepted - and immediately got that sinking feeling that I had screwed up. I had installed SP3 on a number of computers with Intel processors, so I forgot about this glitch with the AMD processor.

The problem is that HP/Compaq got careless when installing Windows XP in the first place, and left it set for an Intel processor, even on computers with AMD.

So, what ya gotta do is go to HP and download the patch that sets Windows XP to recognize the AMD processor. If you haven't installed XP Service Pack 3, install the patch first. If you goofed like I did and get stuck in the reboot loop, reboot in SAFE Mode and then install the patch. When you reboot again, everything should be hunky-dory in normal mode.

This link will lead you to the patch:
http://h10025.www1.hp.com/ewfrf/wc/genericSoftwareDownloadIndex?softwareitem=pv-60484-2&cc=us&lc=en&dlc=en

-Joe-