If you have several Yahoo Messenger Accounts, and want to use them at the same time on the same machine, you can still use Yahoo Messenger GUI. You do not have to use your account in the YM, and then use the other one in the web-based messenger or Yahoo Messenger substitute like GAIM. The substitute will not allow you use some features like buzz, avatar, audible, and background. Even the Webcam can not be used. The default configuration will not let you to perform this action. But with a little modification, it can happen.
1. Click Start, and select Run. You can also press windows+R
2. Type regedit
3. Select HKEY_CURRENT_USER --> Software --> Yahoo --> pager --> test
4. Right click on the test and create a new DWORD value (32 bit)
5. Rename the value as Plural and set its value to 1
And voila! you can use your accounts on the same machine and at the same time.