Normally if you open yahoo messenger and login and again you try to open yahoo messenger by clicking on yahoo messenger program the same yahoo messenger will pop up but after you make changes to your computer as written below if you open one yahoo messenger and click on yahoo messenger program again a new yahoo messenger will open where you can login with another yahoo id.

f you wanna save your time then you can download a software named MULTI YAHOO which is 100% safe and also free..Enjoy:) 

The link is given below:

Download Multi Yahoo

                        OR     

If you wanna go deep into the roots of windows, then here's the another trick:

We are going to edit or change your computer registry values in following trick.

So first of all go to start and click on "Run” And type "Regedit” in the box that opens and hit enter.

Now a new window will open in the left panel of the window search for "HKEY_CURRENT_USER” And expand it keep on expanding or navigating to the following location:

HKEY_CURRENT_USER >
Software >
Yahoo >
Pager >
Test

And after you click on "Test” On the right panel of the window right click and select "new” and "Dword” a new value of name "New Value #1” will be amd ethere now rename it with the following name:

"Plural” without the quotation mark.

Now double click on "Plural” and change the "Value Data” to 1 and click "Ok”

So now you are done setting up!
Now if you open yahoo messenger and again open yahoo messenger a new messenger will open instead of popping up of same messenger.
Now you can enjoy multiple yahoo messengers simultaneously and trick your friends in yahoo chat rooms with multiple yahoo ids.