Go under Adium Preference Pane. You can find it by clicking the Adium text beside the apple or by using keyboard shortcut ,.

And then under the Appearance Tab, search for something called Dock Icon.

Go under Adium Preference Pane. You can find it by clicking the Adium text beside the apple or by using keyboard shortcut ,.

And then under the Appearance Tab, search for something called Dock Icon.

There is a lot of Dock Icons you can choose. Pull Down Menu and Show All... Button contain the same icon.

For better speed, use Pull Down Menu..

However, you can use Show All... Button for better display

Happy Adium-ing.