Hi.
It works now. 2 things: - the squeaksource.com configfile was present in /etc/apache2/sites-availabe but not linked into /etc/apache2/sites-enabled/ - the default site linked into /etc/apache2/sites-enabled/000-default shadowed the squeaksource.com vhost, as it was the default (ie, first) vhost and it shared the server-name box3.squeak.org.
Best -Tobias