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Copy the plugin-wonderful folder to your wp-content/plugins folder and activate it from Plugins -> Installed. Activating the plugin creates a new database table, {prefix}_pw_adboxes, that you can safely remove if you are no longer using the plugin.

Note that if you're upgrading from a pre-0.5 version, you'll have to deactivate and reactivate the plugin. If you're using the Widgets feature of the plugin, you'll have to re-add your widgets to your sidebars again.