Seems some PCs are going into endless reboot loops after installing Windows XP SP3. Both issues seem to affect AMD-based machines, unfortunately. One involves HP machines which, apparently, also run Intel's power management driver by default. The other issue centers around the BIOS, and may be limited to ASUS' A8N32-SLi Deluxe.

Hit the link for Jesper Johannsen's blog. He's a Microsoft MVP, & has posted details of both issues, along with workarounds.