Many thanks Amy,
following your advice and some wordpress instructions i've made a style.css file similar to this one
Theme Name: Twenty Ten
Theme URI: http://wordpress.org/
Description: The 2010 default theme for WordPress.
Author URI: http://wordpress.org/
Tags: black, blue, white, two-columns, fixed-width, custom-header, custom-background, threaded-comments, sticky-post, translation-ready, microformats, rtl-language-support, editor-style, custom-menu (optional)
General comments (optional).
and the theme is now activable from administration panel. :-)
The theme is not working correctly. Do you thing should I put there some instructions to made him working with the other css files that i've put in a daughter folder ?
Thanks and ciao :-)