Stop Windows Messenger in XP or Vista

1. Log on as an administrator.
2. Click Start | Run.
3. In the Run box, type gpedit.msc to open the Group Policy editor. In Vista, you will be prompted to continue. Click the Continue button.
4. In the left pane, under Local Computer Policy | Computer Configuration, expand Administrative Templates and then Windows Components.
5. Double click Windows Messenger.
6. In the right pane, double click the policy "Do not allow Windows Messenger to be run."
7. Click the Enabled option.

Note that Remote Assistance will not be able to use Windows Messenger when you disable it this way.

Copy and paste this into run box

RunDll32 advpack.dll,LaunchINFSection %windir%INFmsmsgs.inf,BLC.Remove

http://www.helpwithwindows.com/WindowsXP/tune-05.html