Some days ago I came accross a problem. I need to use two accounts simultaneously on Google Talk. For some days i used single account. But then i realized this is not a solution. Then i googled it and came with a solution.
Steps are :
1- Create a Shortcut to your Desktop.
2- Right Click -> Properties -> Shortcut Tab -> Target Texbox , add string “/nomutex”.
3- Click Apply and Click Ok.
Now you can run as many instances of Google Talk as you want.