I was investigating some issues this morning integrating dynamically generated GeoRSS with Microsoft's Virtual Earth API. Turns out that the issue is that the API requires appropriate MIME-type for GeoRSS, even when the conent itself is XML. There is an answer...
I think this is simply a matter of how you are setting the MIME type when you generate the file. Here (http://www.geograph.org.uk/syndicator.php?format=GeoRSS) is a sample feed I found on the GeoRSS.org web site. Notice that it is a .php page that auto-generates a GeoRSS file (no .xml extension). It works in my VE mashup without a problem.
The PHP solution is straight-forward. Before spilling out the XML, include this code"
$charset = "iso-8859-1";
$mime = "application/xml";