cocoaforge

To store previous conversations, go to the preferences by choosing "Preferences..." from the "File" menu. Click the "General" tab (the light switch).
The first checkbox "Log conversations" allows you to choose to save conversations.
The conversations are saved in the Library under Application Support>Adium>Users>Default>Logs

If you would like to read previous conversations, press cmd-L or choose "Log viewer" from the "Window" menu.
When a contact is selected, you can immediately go to his or her logs by choosing "View previous conversations" from the "Contact" menu. You can also type shift-command-L

If you would like to you can have some messages of the last conversation shown in the discussion window. You can specify this in the "Advanced" Preferences. Click on "Message history" and choose the options.

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The user is not always "Default", I think users who need this manual will always have "Default" as user, so I don't think it's worth creating confusion by telling users to choose from different users.

The last sentence needs a rewrite, but I can't manage to find a "beautifull" synonym.

There is also an SQL Logger, a web interface for logging that takes a bit of installation and customization to work. If you wish to have many search options and a very nice interface the SQL Logger is worth looking into.

For more information, go to http://www.visualdistortion.org/sqllogger/