Web site access externally

I have installed Magento www.magento.com an e-commerce management system.

I am using COS 6.6 enterprise when I try to access the demo site internally there is no problem but when I go to an external IP address I have problems with access.

The ADSL modem is 192.169.10.1 my server is 192.168.2.1, I have installed magento to when I try to access from an external IP address the browser address bar shows the server address and times out with a server not responding error, if I try to access the site with just the domain name or IP address with out the /magento/ subdirectory I get a directory listing of the html directory which is not good I think and a possible security issue.

Do I need to add an index.php to the html directory to direct to the /magento directory.