Create a shortcut of your Google talk.
Right click the shortcut ----> choose Properties.
In the "Target" you will find this
Code:
"C:\Program Files\Google\Google Talk\googletalk.exe"
Assuming you have installed in C:
Now at the end of target add this " /nomutex " without the quotes.
It should be like this
Code:
"C:\Program Files\Google\Google Talk\googletalk.exe" /nomutex
There is a space after googletalk.exe"
Thats it .Click OK and you can open more than one Google talk