In general, whenever someone uses their Yahoo! id to log-in to their account from a computer, it automatically gets stored in the Yahoo! profiles. These stored ids can be easily accessed from the registry editor as below:
1. Go to Start–>Run… and type regedit and click OK, which open the registry editor window for you.
That’s it!! You have got what you wanted.
Hope this helps…
Try it yourself and post in your valuable comments.
Note: Don’t use this trick for any harassment or spam.