HERE I HVE DONE THIS SEE TWO YAHOO MESSENGER ARE LOGION AT SAME TIME

SPAN style="FONT-SIZE: 18pt">If you are using Yahoo! Messenger v8.0 or above, YahooMulti.reg will let you run multiple copies of Yahoo Messenger.
At the same time which will allow you to login multiple ID’s at the same time.

1) Open Registry Editor (regedit.exe)
Click Start > Run and then type 'regedit' press enter.

2) Then Look For-
HKEY_CURRENT_ USER\Software\yahoo\ pager\Test.

3) Then change this value of plural to like this-
“Plural”=dword: 00000001