Your questions have some difficulties because you don't say if it's v27* or RC* etc.
If it's v27* then forget it because it will never be compatible with any other v27* styles because the user would have to disable borders, background and sub-headers for the blocks in the CMS. And that makes it quite useless.
If it's RC*, then as DrWHO suggests, Floreal will give you some ideas - It may not be totally suitable for what you are trying to do, but ideas nevertheless.
RC*
The two main components of altering the blocks are the style.cfg where you would add new global vars and markup etc, and the cms_block_inc_wrapper.tpl (copied to "Your" style) where you would implement those changes.
Re The spam answer:
I've probably changed / updated some .tpl files and haven't added the MOD script. I had also forgotten to disable registrations again after doing some testing.