How to display Communicator 2007 Chat History
- Click the top-left status button to open the drop-down menu.
- Click Tools > Options
- Go to the Personal tab
- Check on Save my instant message conversations in the Outlook Conversation History folder
- Click OK
- Click Connect, then click Sign Out to log out
- Log back in the application
Your conversations will now be stored.
Also, see here on Finding previos IM Conversations