Download the ZIP file and extract MessengerDisable.exe to your hard drive. You can either double click the EXE file, or create a shortcut to it, as you prefer. You can, optionally, use this utility to remove Windows Messenger from your machine. If you choose to uninstall Windows Messenger on a system with SP1 installed, you will receive an error message about "un-registering" an OCX file. This is normal, and doest not affect the removal process. Windows Messenger will still be removed.
Software that can be used as an alternative to Disable/Remove Windows Messenger Utility: