At this point, we've installed everything we need to install to make Adium look like iChat.
Let's go ahead and go to iChat's preference pane. We'll be configuring the Message Style called iChadium first, so select the Messages tab.
In the Message Style dropdown, select iChadium. And in the Variant, select your color of choice for incoming instant messages. (Note: to randomize the color received in conversation windows, select Incoming Purple).

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Next, select the Appearance tabs to set the Menu Bar Icons, Emoticons and Dock Icons, the Color Theme and List Layout. Select iChat 4 menu bar, the iChat emoticons, then the iChatisation icon from their respective drop downs. In the Contact list section, select
iChat-ish for the Color Theme and List Layout and make sure the Window Style is set to
Regular Window.
You can also go to the Events tab, and create sound effects for certain events, like messages received, sent, and so on. From the Sound set dropdown, you can specify iChat sounds to make Adium sound just like iChat.

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After these configurations, your Adium now looks and sounds like iChat. You now have all the aesthetics of iChat together with the ability to converse with a wider span of contacts that iChat doesn't cover by default.