For some reason the 2 installations --in Debian 3.1-- doesn't created the ISPConfig database.
In the second installation I've created the database manually, but after the installation the database was empty.
I've seen the user (root) and password correct
in the configuration file (/home/admispconfig/ispconfig/config.inc.php).
I've located the db_ispconfig.sql file in the tarball (ISPConfig-2.1.1.tar.gz). I've manually filled up the database:
$ mysql -u root -p ipcdb < db_ispconfig.sql
Seems that ISP Config works, but is possible that come up some problem because the ./install process can't filled up the database?