Ok if it can help somebody...solved the rest of these warnings:
for
Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent in /var/www/webmail/program/include/main.inc on line 61
in /program/include/main.inc
cutted session_start() and putted between line 51 and 53.
for
DB Error in /var/www/webmail/program/include/rcube_db.inc (105): DB Error: connect failed
in /config/db.inc.php
changed "$rcmail_config['db_dsnw'] = 'mysql://roundcube:pass@localhost/roundcubemail';"
to
$rcmail_config['db_dsnw'] = 'mysql://roundcube:password@localhost/roundcubemail';
as mentioned in the INSTALL file.
It runs
and now go to the test of it.