If you’ve got many Gmail accounts and don’t want to keep logging on and off them every time you want to switch account, a simple command line parameter in the Google Talk shortcut can solve your problem. First, create one copy of the Google Talk shortcut on your desktop – leave the original intact. Right-click on this shortcut and select Properties. The Target text box will show you the path of the EXE for Google Talk – something like
“C:\Program Files\Google\Google Talk\googletalk.exe“.
Change this to “C:\Program Files\Google\Google Talk\googletalk.exe”/nomutex and click OK. You will now be able to run multiple instances of Google Talk with different identities for each.