One of the major limitations I’ve found with Yahoo Messenger and Windows Live Messenger is that they allow just single logins. While this provides a bit of security, there are times when you need to login more than one account.

To add multi-user capability:

• Open notepad or any text editor
• Copy + Paste the following:
  REGEDIT4
[HKEY_CURRENT_USER\Software\yahoo\pager\Test]
"Plural"=dword:00000001
• Save the file as Yahoo Multi.reg (Note that you can use any filename, just don’t forget to use *.reg as the extension)
• Alternatively, you can simply download the file here.
• Right click the file and choose Merge or simple double click on the file.