Adding a simple entry to the Windows registry will let you run multiple instances of Yahoo! Messenger simultaneously and sign in to as many accounts as you may have, all from a single user account on the same computer.
- Click Start
- Click Run
- Type regedit in the Open input box and hit ENTER key
- Navigate to:
- Click New on the Edit menu, and then click DWORD Value
- Type Plural, and hit the ENTER key to name the entry.
- In the right pane, right-click Plural, and then click Modify.
- In the Edit DWORD Value dialog box, type 1 under Value data.