Multiple Yahoo Messenger Instance Simultaneously

Type regedit in run command of Microsoft Windows

Look for this string :
HKEY_CURRENT_USER\Software\Yahoo\Pager\Test\

Inside the folder of
HKEY_CURRENT_USER\Software\Yahoo\Pager\Test\
Right click and click new DWORD Value
Double click the DWORD Value and place 00 00 00 01 then press okay

Close Regedit and Test your Yahoo Messenger, try two instance of the program..

Have Fun