Winlogon.exe tar 100% CPU

** STULET **

Does winlogon.exe appear in Msconfig/Startup? If so, then post your log in the Hijackthis forum for assistance.
http://www.bleepingcomputer.com/forums/forum22.html

If this is not malware related then try System File Checker. The main reason for using the SFC utility is when you suspect there may be a problem with a Windows XP system file. SFC allows you to check for any corrupt system files.

Go to Start > Run and type: sfc /scannow

Make sure that you include a space between the c and /. This command will immediately initiate the Windows File Protection service to scan all protected files, verify their integrity, and replace any problem files. If sfc discovers that a protected file has been overwritten, it retrieves the correct version of the file from the %systemroot%\system32\dllcache folder, and then replaces the incorrect file. You must be logged on as a member of the Administrators group to run sfc and it may ask you to insert your Windows Installation CD so have it available.