Open up a copy of google talk on all computers with which you wish to conference. After one copy is opened make a new shortcut for google talk but at the end of it add /nomutex. If you installed it to the default folder then your shortcut should read “C:Program FilesGoogleGoogle Talkgoogletalk.exe” /nomutex. Open 2 instances of the software on every user’s computer. After this start a chain: User 1 should connect on one instance to user 2. User 2 will connect on his second instance to user 3. User 3 will connect using his second instance back to user 1. With this chain everyone is connected to everyone. [via] Link. Or install Skype.
HOW TO conference call with Google Talk