Check out the moinitoring plugin of Openfire. It is also archiving the conversations, e.g. for external auditors (think about SOX compliance or anti trust measures). It ist pretty raw, but is doing what you want to: IT gets you the conversation data.
Monitoring plugin is called “Monitoring Service” and as Michael mentioned you can find it on the Available plugins page in Admin Console.
There is no working tool for reading audit logs currently. You will have to code one yourself. You can use the source of the previously created tool by a community user http://community.igniterealtime.org/docs/DOC-1874 (the source is in the zip file)