Windows Messenger 4.5 or Later on Either Windows XP Home or Windows XP Professional
1) Click on Start, Run
2) Type REGEDIT and Press Enter
3) Click on the Pluses (+) next to the following items
HKEY_LOCAL_MACHINE
Software
Policies
Microsoft
4) If the folder Messenger is not listed, click on the Edit menu, point to New, click Key, and then type Messenger for the name of the new registry key
5) If the folder Client is not listed under Messenger, click on the Edit menu, point to New, click Key, and then type Client for the name of the new registry key
6) On the Edit Menu, point to New, click DWORD Value, and then type PreventRun for the name of the new DWORD value. Remember all of this is case sensitive.
7) Right-click the PreventRun value that you created, click Modify, type 1 in the Value data box, and then click OK.
8) Quit Registry Editor.