Re: how to create theme myself
you need to edit Smarty templates (tpl files, that you'll find under ./templates/ directory. The default ones are in that directory (for updated themes such as tinineat style), but some more specific are inside subdirs of ./templates/styles/newtheme (those tpl in there override the default ones in base directory)
Moreover, you have to create a modified .css file than the ones in ./styles, and it needs to have the same name than your subdirectory under ./templates/styles.
I think that you can find some more info on http://dev.tikiwiki.org on how to modify .tpl files , and search also http://themes.tikiwiki.org , and http://doc.tikiwiki.org for styles, themes, etc.
Cheers, and good luck!
xavi