You Can Login With Multiple Id'S On The Same Yahoo Messenger Without Any Download Or Patch.
1. Follow These Steps
2. Go To Start Then Run . Type Regedit, Then Enter .
3. Navigate To Hkey_Current_Usersoftware\Yahoo\Pager\Test
4. On The Right Pane , Right-Click And Choose New Dword Value .
5. Rename It As Plural.
6. Double Click And Assign A Decimal Value Of 1.
Now Close Registry And Restart Yahoo Messenger .For Signing In With New Email ID