I moved your post to the Tune-up folder.
It sounds like you encountered a problem with Windows XP SP3, as the symptom you are describing has been known to affect HP and Compaq computers with AMD processors.
The solution can be found at the XP Solution Center:
XP Solution Center - http://support.microsoft.com/ph/1173#tab2
You can also seek help for Windows Update problems via the
Windows Update Solution Center - http://support.microsoft.com/ph/6527
And, support for OneCare can be had per these instructions:
How to reach support (FAQ) - http://forums.microsoft.com/WindowsOneCare/ShowPost.aspx?PostID=2421771&SiteID=2
-steve