u don't need to download anything but simply change the command line parameter.....

like this

1)Right click on the Google Talk shortcut.
2)click on Properties.
3)Go to Shortcut tab on Google Talk Properties window.
4)On the Target textbox, add in the /nomutex to the end of the line so that it looks like below (or you can simply copy and paste the below syntax and replace the original).
“c:\program files\google\google talk\googletalk.exe” /nomutex
5)Click on OK.

i didn't have to do anything after this nd clicking on the shortcut multiple times just gave me different googletalk window

however if that don't work then just try this out!!!!

To create a new shortcut for Google Talk:

1)Right-click on the desktop or anywhere you want to place the GTalk shortcut.
2)Select New on the right click context menu.
3)Then select Shortcut.
4)Copy and paste the following line to the text box when prompted to type the location of the item:
“c:\program files\google\google talk\googletalk.exe” /nomutex

5)Click on Next.
6)Give the shortcut a proper name such as Google Talk or Google
Talk Multiple or Google Talk Polygamy.
8)Click OK until you are done.

If you have hex editor, you can act like a hacker and modify the bits in Google Talk program so that it will always allow multiple instances of GTalk to be launched whether the /nomutex switch is specified or not.

Launch hex editor and open googletalk.exe, then search for the following patterns in the hex editor:

004536FD . 3BC6 CMP EAX,ESI
004536FF . 75 05 JNZ SHORT googleta.00453706

Modify the string to look like the following:

004536FD . 8BC1 MOV EAX,ECX
004536FF . EB 05 JMP SHORT googleta.00453706