Assuming you have a working instance of Omeka 2.0 somewhere, the only files you actually need in a theme are:
· css/style.css
· theme.ini
Themes in Omeka will use the core templates found in application/views/scripts, unless your theme specifically includes any. So, by adding 'css/style.css' to your theme, Omeka will load that file instead of the one in application/views/scripts. See "Understanding Default Theme Files" at
http://omeka.org/codex/Understanding_Default_Theme_Files for more info.
You can see a full list of these templates for Omeka 2.0 at
https://github.com/omeka/Omeka/tree/master/application/views/scripts. Omeka 2.0 is still under development, so I'm not sure how stable the templates (and the functions they use) are at the moment. If you regularly pull updates from the master branch, you should be able to keep up with changes just fine, and incorporate changes into any additional templates you'd want to override in your theme. (This is a case where it's handy to watch the "History" of a particular directory through Github, like
https://github.com/omeka/Omeka/commits/master/application/views/scripts). Otherwise, just edit the css/style.css file in your theme, and rely on the core template files for everything else.
Best,
Jeremy