Missy,
I moved your post here as it was unrelated to the other thread you posted in. Please start new topics if you have new questions.
As for your questions:
1) The file you want to edit is the block.unregistered.php file which is in your JomSocial templates folder for whatever template you have selected. In there, you can remove whatever portions of the form you want to.
2) To add your own script, you'll need to add code like the following, which will insert a custom image that can be clicked on to login:
<a href="javascript:void(0)" onclick="jfbc.login.login_custom();"><img src="http://cdn.sourcecoast.com/linktoimage.jpg" /></a>
You won't be able to add the standard "Login With Facebook" button because of how that popup is displayed, which prevents Javascript from running.
For more information, or other examples see the "Can I use a custom image for the Login With Facebook button?" question in our Common Support Question area:
www.sourcecoast.com/jfbconnect/docs/common-support-questions
Hope that helps,
Alex