Follow these steps:

1. Go to Start ==> Run. Type regedit and then enter.
2. Navigate to: HKEY_CURRENT_USER ==> Software ==> yahoo ==> pager.
3. On the right pane, right-click and choose new ==> Dword value.
4. Rename it as Tabbed IM.
5. Double click and assign a decimal value of 1.

That’s it done!! Now close registry and restart Yahoo! Messenger. Finally…

I have only tested this trick in Yahoo! messenger v8.1, so can’t confirm whether it works in other versions or not. Also you might face a few GUI glitches which can be fixed by maximizing/minimizing the chat window.

By default you can only use a single Yahoo! ID to log into Yahoo! messenger and if you try to run another instance of messenger, it’ll not run. But here I’ll tell you a very simple and small trick to enable multi-login feature in Yahoo! messenger and you’ll be able to run multiple instances of Yahoo! messenger and log into separate Yahoo! accounts without any problem and without using any 3rd party utility.

Follow these steps:

1. Go to Start –> Run. Type regedit and then enter.

2. Navigate to: HKEY_CURRENT_USER –> Software –>yahoo –> pager –> Test.

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

4. Rename it as Plural.

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

That’s it done!! Now close registry and restart Yahoo! messenger. For signing in with new id open another messenger.