How to Change Theme Options Per Blog

Hi -

Thanks for a great service here. A couple of questions about themes. I am very familiar with creating and editing themes on single WP installations, and have been looking at the MU setup -- including reviewing FTP directories.

QUESTIONS:
1. If we used a theme like Home » WPMU Nelo, can different blogs have different settings and use different header images, etc.? If so, and we had 10 users using the same theme, where would the different header images be located via FTP directories?

2. If we want to use a parent/child theme strategy, and the child theme offers a theme option to upload a custom header image, can the parent be loaded sitewide, then just one childtheme sitewide, or must a different named version of the same child theme be loaded manually in order to have different options?

Thanks -
Scott