I came across this information IN A PCWORLD NEWSLETTER  by PC World columnist Steve Bass January 4 2006.

 Is this a " Microsoft hotfix" that should be applied to my dual proccessor XPS system ? 

 "If your motherboard has multiple processors that support specific processor power management features, your system will experience decreased performance. Or in Microsoft's quaint way of putting it, "unexpected behavior."

"Here's my (his) story. My Intel motherboard has dual-core processors. A while back I noticed a slowdown--sluggish access opening files and loading apps. I did the usual: scratched my head a lot, cleaned my Temp and Internet cache folder, ran anti-spyware and antivirus scans, defragged the hard drive, and said nice soothing things to the computer. "

"Apparently enough people have complained, so Microsofts posted an article to address the problem,  the company's posted a hotfix. The details are in a concisely titled Microsoft Knowledge Base article: "Computers that are running Windows XP Service Pack 2 and that are equipped with multiple processors that support processor power management features may experience decreased performance":
http://support.microsoft.com/default.aspx?scid=kb;en-us;896256