The feed location is defined in the config.xml file in code/core/Mage/AdminNotification/etc/config.xml

It is not good practice to change the data in this file, instead either add the config data to the XML configuration file of an existing module or add a new entry to the database to override the value.

All of the configuration data is stored in core_config_data. Add an entry to the table using the SQL,

INSERT INTO core_config_data</pre>
SET(scope='default', scope_id=0, path='system/adminnotification', VALUE='uri')

The RSS must follow the following pattern.

<?xml version="1.0" encoding="UTF-8"?></pre>
<rss version="2.0" xmlns:atom="http://www.w3.org/2005/Atom">
<channel>
<title>My Custom Notifications</title>
<atom:link href="http://notifications.screenpages.com/?feed=rss2" rel="self" type="application/rss+xml" />
<link>http://mysite.notifications.com</link<!-- Source uri -->>
<description></description>
<copyright>Copyright (c) 2009 My company</copyright>
<webMaster>me@email.com</webMaster>
<language>en</language>
<lastBuildDate>Fri, 19 Jun 2010 16:20:05 +0000</lastBuildDate>
<item>
<title>Title</title>
<link>http://notifications.xxx.com</link><!-- link to the message -->
<severity>3</severity> <!--severity level between 1 and 4 -->
<description><![CDATA[Your content]]></description>
<pubDate>Fri, 19 Jun 2010 16:04:38 +0000</pubDate>

</item>
</channel>
</rss>