Nice one! That's what I'm working on at the moment

However, I'm trying to create a new section for theme. Was contemplating moving custom fields to the same page to too to keep all the bits that allow users to alter the appearance together.
Regarding the header.txt well I was thinking of allowing admins to edit it within their browser as opposed to simply linking to it if you see what I mean... Could do the same thing with the footer.txt then too
Once we are able to edit these within the site itself then I don't see why we couldn't also have multiple header.txt's and footer.txt's and select the ones we want from a drop down list bringing us closer to having themes.. Also, if we could have a HTML editor with simple bbcode such as bold, italic, underline and add URL or pictures etc.. It would then make it easier for non-ciders to edit their themes
Post up the code you've used so far to have the header image and header.txt