Some times there may be situations that you want to chat with two different Yahoo! Messenger IDs simultaneously, for example, one with your office coworker and other with your friend. Normally this is not possible.
If you have two Yahoo! Messenger IDs, here is a simple way to chat with multiple IDs.
Yahoo Multi Messenger is a small patch for your Yahoo Messenger to run multiple instances. This portable utility patches Yahoo Messenger 10 and lets you run as many instances of the chat client as you want.