eZ relies on a set of template files, css files and more (images, javascript). Check out /design/standard/ in a default eZ install to get an idea on the file structure of an eZ design/theme.
Now for Dreamweaver; I'm not sure what you mean by "making them communicate" but changing a design in eZ usually means altering one or more of those template files. This can be done with Dreamweaver (DW), there is actually a DW extension for this, see http://share.ez.no/articles/ez-publish/development-tools-for-ez-publish/%28page%29/3. I'm not sure if this still works in recent DW versions though, the extension might be outdated.
There is also documentation available about the templates. See http://ez.no/doc/ez_publish/technical_manual/4_x/templates.
If my reply does now answer your questions, please elaborate and we'll try to give you more information on templates.
Regards Robin
Board member, eZ Publish Community Project Board - Member of the share.ez.no team - Key values: Openness and Innovation.
