I use mysql with postfix (from howto http://www.howtoforge.com/virtual_postfix_mysql_quota_courier ) So what should I answer to "Virtusertable-File" and "Local-Host-Names-File" during installation?
ISPConfig is not compatible with the virtual user howto. Either you configure your server accordinf´g one of the perefct setup howtos or you did not install ISPConfig.