On the "New Medium" page, the hint-text below the input boxes look like this:

The path to the medium, can be a URL or a valid NFS server (exclusive of the architecture).
for example <em>http://mirror.averse.net/centos/$version/os/$arch</em> where <strong>$arch</strong> 
will be substituted for the host's actual OS architecture and <strong>$version</strong>, 
<strong>$major</strong> and <strong>$minor</strong> will be substituted for the version of the operating system. 
Solaris and Debian media may also use <strong>$release</strong>.

So the STRONG-Tag is not parsed correctly. Also an example for a NFS-Server entry would be helpful