Uninstall Windows Messenger

Click Start > Run and in the Open: box type the following command (press OK when done):

RunDll32 advpack.dll,LaunchINFSection %windir%\INF\msmsgs.inf,BLC.Remove

You can just copy/paste the command above in the Open: box from the Run command.

Note: If you have Windows XP Service Pack 1 installed, you'll receive an error message.  Just click OK, Windows Messenger will be removed anyway.