I'm confused, but that's normal for me.  I'm not sure what you mean by wanting to add a new feed to your opml.  Also, the feed link you give gives me nothing, however, when I use this one:

http://www.feed-project.eu/rss.aspx

I can see an RSSv2.0 feed using custom namespaces.  (I view the source to inspect it)

<rss version="2.0"
    xmlns:atom="http://www.w3.org/2005/Atom"
    xmlns:cf="http://www.microsoft.com/schemas/rss/core/2005"
    xmlns:media="http://search.yahoo.com/mrss">
    <channel>

Now, where the trouble seems to be located is in the item description elements.  This tag is using a custom namespace descriptor cf:type, which will not translate using the default xsl in the News Feeds (RSS) module newest version.   So, whenever a xsl encounters a tag it doesn't understand it will by pass it.

        <item>
            <title>FEED Review, Brussels</title>
            <description cf:type="html">FEED Intermediate Review,&amp;nbsp;30&amp;nbsp;January 2009,&amp;nbsp;Brussels</description>
            <pubDate>Thu, 29 Jan 2009 22:00:00 GMT</pubDate>
            <link>http://www.feed-project.eu//Default.aspx?page=newsdetail&amp;ListID=30&amp;RowID=22</link>
        </item>

I lost my test environment at home, so I can't double check this situation.  However, when I check the feed using Xselerator and using the default.xsl to render it, it works, so maybe that's not really the issue.  Let me know if the link is correct, and if all of the descriptions appear that way for you.  Also, tell me how you set up the module.

I tried using the http://skoussouris.googlepages.com/feeds-v2.opml in the module, and it does not load. 

Feed 'http://skoussouris.googlepages.com/feeds-v2.opml' could not be loaded. Error: The element 'channel' has incomplete content. List of possible elements expected: 'title, link, description, language, copyright, managingEditor, webMaster, pubDate, lastBuildDate, category, generator, docs, cloud, ttl, image, textInput, skipHours, skipDays, rating, item' as well as any element in namespace '##other'.

The new module is supposed to work for OPML, but it's not working for this one.  You might want to add it to the list of feeds not working in the thread at the top of the News Forum, 'Post Your Broken Feeds Here', to have Peter check into it.

For the other feed, it is showing up 2 items w/o issue.  (See example)

=====Example Rendering=========

AMCIS Conference, San Francisco

Wed, 05 Aug 2009 21:00:00 -0500

15th Americas Conference on Information Systems (AMCIS)
San Francisco, California, August 6 - 9, 2009

Call for Papers: AMCIS Mini-track: Worldwide Advances in eGovernment Interoperability

FEED Review, Brussels

Thu, 29 Jan 2009 22:00:00 -0600

FEED Intermediate Review, 30 January 2009, Brussels

=====End Example Rendering ==============

So, not sure what is going on for your implementation.  Can you tell us about your configuration and news module setup?