Preventing the default Windows Messenger from running.

To disable the in-built Windows Messenger on XP

1. Login as administrator
2. Start > Run
3. Type gpedit.msc in the dialog box, Press Enter.
4. Now you can see the "Group Policy" window, from the Tree View thats shown at the left, Select Computer Configuration to disable it for all users or Select User Configuration for disabling only for your account.
5. Select Administrative Templates > Windows Components > Windows Messenger
6. Next double click the Setting to enable both "Do not allow Windows Messenger to Run" and "Do not Automatically start windows messenger initially".
7. Your done. If its already running, exit.

The default windows messenger is as good as removed now. If you want to save the disk space too then remove windows messenger by uninstalling it from the control panel > Add/Remove Programs > Add/Remove Windows Components.