If you're not using the SCLogin module (which is fine), then instead of the {JFBCLogin} tag, you'll have to use the following HTML:
<a href="javascript:void(0)" onclick="jfbc.login.login_custom();"><img src="/path-to-button-image.jpg"/></a>
You can take a screen shot of your current button or use another Facebook-type image if you'd like. The above will function just the same as your current button though.
Sorry for the troubles, and let me know if you need more help,
Alex