The center column of radio.indymedia.org is a dynamic listing of stations currently broadcasting, including stream quality and number of listeners. To generate this list, it uses Icecast's public broadcasting functionality. To add your stream to the list, you need to be broadcasting with Icecast (or relay your non-Icecast stream on an Icecast server), and have access to your Icecast server's configuration file, typically icecast.xml.
To add your stream to the listing, add this to your icecast.xml:
<directory>
<yp-url-timeout>15</yp-url-timeout>
<yp-url>http://radio.indymedia.org/cgi-bin/yp-cgi</yp-url>
</directory>