Here is the trick to do so:
1. Create a shortcut in the desktop.
2. Right Click and Click the Properties.
3. Go to Shortcut Tab.
4. Edit the Target Column as “C:Program FilesGoogleGoogle Talkgoogletalk.exe” /nomutex instead of the original “C:Program FilesGoogleGoogle Talkgoogletalk.exe” /startmenu.
5. Apply the changes and Save it.
Now, you are ready to use as many google talk as you want by just clicking on it and signing to as many accounts.