Microsoft Office Communicator 2005 doesn’t have automatic client chat logging facility. But it is possible if you can click on save as email during the chat session. But during this time, you may forget to save.
Another way, you can use Instant Archive Viewer for LCS/OCS. For IAV, please link here.
Also you may try to activate a logging feature of Outlook 2007, so that Communicator writes a chat-log into an Outlook folder. Thus you can view your chat log in Outlook.
You can use “MOC Client Logger” a small tool, that fulfills ur purpose. Just download and after install you can do what you want! This link is here.
Please update me on further proceed.