Quote:
Explorer.exe Process Uses Many CPU Cycles When Windows Is Idle
View products that this article applies to.
SYMPTOMS
Under certain circumstances, the Explorer.exe process uses an excessive number of CPU cycles when Windows is idle, and as a result, Windows performance is degraded.
NOTE: To view the CPU cycles that the Explorer.exe process uses, right-click a blank area on the taskbar, click Task Manager on the shortcut menu that appears, and then click the Processes tab.
RESOLUTION
To resolve this problem, obtain the latest service pack for Windows XP. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:
Sounds like you don't have the most up to date patches from MS, I would go so far as to say you still have SP1, and when you reinstall you should have SP2 handy, because as soon as you connect to the internet, you are going to within 10 minutes have the bad guys knocking on your door..