No, I don't think you understand. The base SFC plugin, once activated, takes care of the FeatureLoader and that FB.init stuff for you. You don't need to add any of that manually at all. And you definitely don't need the xd_receiver.htm file on your site, that's handled by the plugin internally.
Install and setup the base SFC plugin. Then just use the fb:login-button code anywhere. In the theme, in a post, in a widget... whatever you like.
If you have a custom page or theme or what not, then make sure it includes the proper calls to wp_head() and wp_footer() to get the Facebook code inserted into it.
If you're making a custom login page, then activate the SFC-Login plugin and make sure you page runs the login_form action, like the normal login page does. That will have the login plugin insert the login button as per usual. Also, the Login plugin has other code to make the button actually work. :)