Sub pages result in 404
Sounds like the problem is that clean URL's are enabled in Drupal but not supported by your Apache configuration (make sure that mod_rewrite is enabled and the folder/vhost has AllowOverrides enabled) or the .htaccess file is missing.

You can verify that this is the problem by accessing the non-clean version of the URL. For example, instead of example.org/something, try example.org/?q=something.

See http://drupal.org/getting-started/clean-urls for more information.