Are you comfortable editing your theme's *.tpl files? If so, please add the following as the first line of entries.tpl or index.tpl assuming this is not yet a site with any visitors:
Your category problem does not appear to be related to the Timeline theme, but you can verify that by switching themes to 2k11 to see if the problem continues or is solved.
If your preference is the Timeline theme, but you want this banner behavior from Cleanblog, it should be possible. Otherwise it is just a matter of trial and error to get it to work. PM me if you need additional assistance.
Not sure the method above will work for retrieving the image... maybe this will: {else} {assign var=random_id value=1|mt_rand:5} <style type="text/css">.intro-header {ldelim}background-image: url('{$serendipityHTTPPath}templates/{$template}/img/background{$random_id}.jpg');{rdelim}</style> {/if}
Am I understanding you correctly: You want to use the timeline theme, but display a category specific sub header on entry pages instead of the same sub header on all pages? If so, it might be fairly easy. In index.tpl is this: {* SUBHEADER IMAGE *} {if $template_option.subheader_img} <style type="te...
Do you have any hints how you structured the add-on (caveat for certain files etc)? No worries if you don't have it at hand, I'll look it through otherwise. I'm not really sure what you are asking. However, I have a prototype running on the Timeline demo site now which allows images to be assigned ...