Back up the following locations/items and you should be good to go:
~/Library/Preferences/com.adiumX.adiumX.plist
~/Library/Application Support/Adium 2.0/
Where ~/ is your home directory (for example, /Users/[your user name]).
This will back up the preferences and the instant message logs, plus any dock icons/menu bar icons/sound schemes/contact list styles/message styles/other extras that you've installed for Adium. So you will be back up and running in no time! 🙂