Computerworld reported yesterday in their story "HP confirms XP SP3 endless reboot snafu, promises patch" that...
"... some users of its AMD-based desktops have had problems after installing Windows XP Service Pack 3 (SP3), and said it would issue a patch this week to prevent machines from spiraling into endless reboots. HP also told users to delay installing XP SP3 until that patch was released."
Microsoft is also working on a hotfix for this issue, and will be available after it has been rigorously tested and meets our quality bar for release.
Computerworld also notes that "users impatient with HP's or Microsoft's patch plans can instead download a free tool... that detects and fixed PCs that may be susceptible to the endless reboot issue."