Disable Windows® Messenger in Windows® XP Pro

If you're running Pro, you can use GPEDIT.MSC to prevent Messenger from loading. Otherwise, even disabling it in startup won't cause it to "always" not run. Outlook, OE and some MS web pages can still make it load.

1) Start, Run and enter GPEDIT.MSC  
2) For "per machine" restriction, go to Computer Configuration, Administrative Templates, Windows Components, Windows Messenger
  For "per user" restriction, go to User Configuration, Administrative Templates, Windows Components, Windows Messenger
3) You can now modify whether it starts initially and/or whether its to run at all.

Note: Outlook and Outlook Express will take longer to open, unless you turn off Messenger Support. In Outlook Express its in Tools, Options, General tab. In Outlook its in Tools, Options, Other. One additional Registry edit is needed to prevent a serious delay in opening OE if you use the Contacts Pane and have disabled or removed Messenger.