Customizing the FB Fanbox is an extreme pain in the behind.
If you want to do it, you can pass a custom CSS URL to it. More info here: http://wiki.developers.facebook.com/index.php/Fb:fan
I can help you out a bit with some of the starting CSS Classes to use:
.connect_widget .connect_widget_facebook_logo_menubar {
}
.fan_box .full_widget .connect_top {
}
.fan_box .full_widget .page_stream {
}
.fan_box .full_widget .connections {
}
That references the four different sections.