hehe..
i'd like to share this one..
now..u can do something new to your Yahoo Messenger..

Login with Multiple IDs at the same time in Yahoo Messenger

Step 1- Go to Start > Run > type regedit and press enter.

Step 2 – Go to HKEY_CURRENT_USER > Software > Yahoo > pager > Test

Step 3 – On the right pane > right-click and choose new Dword value .

Step 4 – Rename it as Plural.

Step 5 – Double click and assign a decimal value of 1.

Step 6 – Now close registry and restart yahoo messenger.

Step 7 – For signing in with new id open another messenger .

Enjoy!

source :http://www.hacktrix.com/login-with-multiple-ids-at-the-same-time-in-yahoo-messenger