You have a virus. One that your AV software is not catching. See
www.dougknox.com, Win XP Utilities, Create Emergency Copies of Critical XP
System Utilities. This small VB Program will create backup, usable copies
of Task Manger, Regedit and MSConfig (named Taskmgr1.exe, Regedit.com and
MSConfig1.exe) in a new folder C:\EmergencyUtil. Many virus programs will
intercept these programs, based on their original file name. The modified
file names, allow them to be run. Open Windows Explorer to C:\EmergencyUtil
and double click the application you need. The next revision will allow you
to browse for the folder you want to place the backups in.
Additionally, see the Win XP Utilities section for Startup Programs Tracker.
This small utility scans your system for startup programs and running
processes. It also allows you to create a log file that can be copied and
pasted into a newsgroup post. The contents of the program window are also
copied to the Windows Clipboard, automatically. For replies to newsgroup
posts, do NOT include the Running Services, unless its absolutely necessary.
Then update your AV software and scan your system again. If possible, scan
your system from Safe Mode.