Just follow the steps below:-
Step 1:-Go to start>run
Step 2:-type regedit
Step 3:-go to HKEY_CURRENT_USER
Step 4:->Software>yahoo>pager>test
Step 5:-Right Click New> DWORD Value and name the new file "plural".Doube click it and change from 0 to 1 .
Now you would be able to open unlimited Yahoo messengers with the help of this simple trick.The same trick can be applied to other platform like Skype,msn,gtalk aswell by changing the software in step 4.

