1. Start Registry Editor (Regedit.exe).
2. Locate and click the following registry key:

   HKEY_LOCAL_MACHINE\Software\Policies\Microsoft

3. On the Edit menu, point to New , click Key , and then type Messenger for the name of the new registry key.
4. Locate and click the following registry key:

   HKEY_LOCAL_MACHINE\Software\Policies\Microsoft\Messenger

5. On the On the Edit menu, point to New , click Key , and then type Client for the name of the new registry key.
6. Locate and click the following registry key:

   HKEY_LOCAL_MACHINE\Software\Policies\Microsoft\Messenger\Client

7. On the Edit menu, point to New , click DWORD Value , and then type PreventRun for the name of the new DWORD value.
8. Right-click the PreventRun value that you created, click Modify , type 1 in the Value data box, and then click OK .
9. Quit Windows Messenger.

This tip is extracted from article Q302089 of the Microsoft Windows XP Knowledge Base.