Freeyland, if you want to read namespaced elements (qname) best practice would be to use Xpath. You could try out some query such as ;
$conditions = $xml->xpath("//yweather:condition");
But to make the whole process easy I've made an update to the mashups module which could handle such feeds. You can download the latest build in the trunk of mashups module and try out the following code. This will fetch the attribute values of condition tag in Yahoo Weather feed.
In your controller;
$yw = new RestfulService("http://weather.yahooapis.com/forecastrss");
$params = array(
"u" => "c",
"p" => "USIL0225"
$conn = $yw->connect();
$result = $yw->searchAttributes($conn, "//yweather:condition");
and in the template;
<% control YahooWeather %>
<p>weather conditions for $date<br/>
$text - tempreature -$temp</p>
<% end_control %>
Hope this helps :)
>>Is there a way to cash the output?
Currently Mashups module doesn't support caching, but it's something on the road maps for future releases.