Packages can be installed silently using the -quiet command line option

Specifying this option causes the package to run silently, i.e. no dialogs are displayed to the user.

For additional command line options see the following Knowledge Base article:

Title: Command Line Options for 7.0 Packages
URL:http://pharos.custhelp.com/cgi-bin/pharos.cfg/php/enduser/std_adp.php?p_faqid=561&p_created=1137078662