The submit_news.php iframe is hardcoded - you can change the target in the options. The "Contact Page Link" option in the ""Newscast" General Options" tab is applied to the white letter symbol on the top right (next to the social icons). The "Contact Page" in the "ontact & Submit Member News" options tab allows you to select a contact page which won't open in an iframe/popup like the "submit news form" but which will be displayed on the page you select - i.e. like the demo here: http://www.kriesi.at/themes/newscast/contact/
To change the submit news iframe target open up header.php and search for:
<a id='submit_news' rel="prettyPhoto" class='ie6fix' href="<?php echo get_bloginfo('template_url'); ?>/submit_news.php?iframe=true&width=420&height=580"><?php _e($k_option['contact']['submit_news_text'],'newscast'); ?></a>
Replace the href attribute content with any other path/url (i.e. replace submit_news.php with another file, or link to an external website, etc.). You can change the size (height/width) of the popup/iframe too.