Using DNN 5.1

I have a piece of java script that isn't working correctly in DNN although I can get it to work in a simple HTML page


<!-- Start Rightnetworks.com Login -->
<script type="text/javascript" src="http://www.rightnetworks.com/js/login...>
<script type="text/javascript">rightnetworks_forma();</script>
<!-- End -->

This script displays a login form - username field, display screen size select and check box to upload/download files.
When I enter a username, the username field is cleared and the login page is not displayed.

Any help getting this to work is appreciated.

Thanks.