Shoutbox

• Close every instance of Messenger by right-clicking the systemtray icon and choosing "Exit".
  
  
• Kill all the Messenger Plus! 3 processes:
  
  1. Press CTRL-ALT-DEL to open the Windows Task Manager
     
  2. Find every process named: msgplus.exe and kill it by right-clicking on it and choosing "Kill process tree"
  
  
• Open Windows Explorer and completely remove the Messenger Plus! installation directories:
      for Messenger Plus! 3 this is by default: "C:\Program Files\MessengerPlus! 3"
      for Messenger Plus! Live this is by default: "C:\Program Files\Messenger Plus! Live"
  
  
• Still in Windows Explorer, go to the MSN Messenger installation directory (by default: C:\Program Files\MSN Messenger) and delete the file called "msimg32.dll".
  
  
• Still in Windows Explorer, completely remove the data directory of Messenger Plus:
      by default: "C:\Documents and Settings\All Users\Application Data\Messenger Plus!"
  
  
• Open your registry editor by going to your Windows Start menu > Run > regedit
  
  
• In the Registry Editor navigate to and delete the following keys and values:
     
      HKEY_CURRENT_USER\Software\Patchou
      HKEY_LOCAL_MACHINE\SOFTWARE\Patchou
  
      HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Windows\AppInit_DLLs
      (only if AppInit_DLLs contains "MsgPlusLoader.dll")
  
      HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
      (remove only stuff related to Messenger Plus! here)
      HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
      (remove only stuff related to Messenger Plus! here)
  
  
• Reboot your computer

If you done everything listed here correctly, then everything related to Messenger Plus! is removed from your computer without using the uninstaller.

Note that the directories listed can be slightly different for you. I've just listed the default ones.

(Though some redundant regisrty settings might still exist, like the entry in your Add/Remove Programs config panel)