Do you have friends or colleagues on different Google Talk accounts that you need to chat simultaneously or you have different Accounts of Google Talk for Personal and Professional use and need to login to both of them simultaneously.
One way to do the above would be to use the Chat feature in Gmail for one account and Google Talk client for the other.
What if you need to login to more than two accounts or You have the chat feature in Gmail turned off and don't want to use it, in that case you can use the below methods to login to multiple accounts at once.
Assuming that you have Google Talk installed under C drive in the below location,
Go to Start->Run and type "c:\Program Files\Google\Google Talk\googletalk.exe" /nomutex and click ok, repeat this to open any number of Instances that you may want.
Create a shortcut of the Google Talk icon on your desktop if you don't have one.
To create a shortcut, right click on the Google Talk icon in your start menu and click on send to-->Desktop(shortcut).
Right click on the Google Talk messenger icon and select the Properties option.
Modify the text in Target location to "C:\Program Files\Google\Google Talk\googletalk.exe" /nomutex (replace startmenu with nomutex) and click OK.
Now you can use that shortcut to launch multiple Instances of the Google Talk Client.
Let me know in the comments if you have any Issues implementing the above methods.
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