<A HREF="http://zdnet.com.com/2100-1103_2-5326707.html?tag=zdnn.alert">A problem in the Service Pack 2 update</A> for Windows XP may keep owners of AMD-based computers from using the long-awaited security package under certain circumstances. In an article posted in the Knowledge Base section of its Web site, Microsoft says that Service Pack 2 may not work with computers running Advanced Micro Devices' 64-bit microprocessors.