Gracias por tu respuesta... lo de namespace() no me lo sabia

#
Al final lo resolví así:
[AS3]
private function xmlCargado(e:Event):void
{
clima_xml = new XML(e.target.data);
var lista1:XMLList = clima_xml.results.channel.elements();
_ciudad = String(lista1[6].@city)
var lista2:XMLList = clima_xml.results.channel.item.elements();
_recurso = String(lista2[7].namespace());
}
[/AS3]
por cierto mi xml completo era este.....
Código XML :
<?xml version="1.0" encoding="UTF-8"?>
<query xmlns:yahoo="http://www.yahooapis.com/v1/base.rng"
yahoo:count="1" yahoo:created="2012-04-25T00:35:30Z" yahoo:lang="en-US">
<results>
<channel>
<title>Yahoo! Weather - Viacha, BL</title>
<link>http://us.rd.yahoo.com/dailynews/rss/weather/Viacha__BL/*http://weather.yahoo.com/forecast/BLXX0018_f.html</link>
<description>Yahoo! Weather for Viacha, BL</description>
<language>en-us</language>
<lastBuildDate>Tue, 24 Apr 2012 8:02 pm BOT</lastBuildDate>
<ttl>60</ttl>
<yweather:location
xmlns:yweather="http://xml.weather.yahoo.com/ns/rss/1.0"
city="Viacha" country="BL" region=""/>
<yweather:units
xmlns:yweather="http://xml.weather.yahoo.com/ns/rss/1.0"
distance="mi" pressure="in" speed="mph" temperature="F"/>
<yweather:wind
xmlns:yweather="http://xml.weather.yahoo.com/ns/rss/1.0"
chill="41" direction="250" speed="7"/>
<yweather:atmosphere
xmlns:yweather="http://xml.weather.yahoo.com/ns/rss/1.0"
humidity="81" pressure="30.56" rising="0" visibility="4.97"/>
<yweather:astronomy
xmlns:yweather="http://xml.weather.yahoo.com/ns/rss/1.0"
sunrise="6:44 am" sunset="6:19 pm"/>
<image>
<title>Yahoo! Weather</title>
<width>142</width>
<height>18</height>
<link>http://weather.yahoo.com</link>
<url>http://l.yimg.com/a/i/brand/purplelogo//uh/us/news-wea.gif</url>
</image>
<item>
<title>Conditions for Viacha, BL at 8:02 pm BOT</title>
<geo:lat xmlns:geo="http://www.w3.org/2003/01/geo/wgs84_pos#">-16.65</geo:lat>
<geo:long xmlns:geo="http://www.w3.org/2003/01/geo/wgs84_pos#">-68.3</geo:long>
<link>http://us.rd.yahoo.com/dailynews/rss/weather/Viacha__BL/*http://weather.yahoo.com/forecast/BLXX0018_f.html</link>
<pubDate>Tue, 24 Apr 2012 8:02 pm BOT</pubDate>
<yweather:condition
xmlns:yweather="http://xml.weather.yahoo.com/ns/rss/1.0"
code="11" date="Tue, 24 Apr 2012 8:02 pm BOT"
temp="45" text="Light Rain"/>
<description><![CDATA[
<img src="http://l.yimg.com/a/i/us/we/52/11.gif"/><br />
<b>Current Conditions:</b><br />
Light Rain, 45 F<BR />
<BR /><b>Forecast:</b><BR />
Tue - Showers. High: 54 Low: 38<br />
Wed - AM Showers. High: 59 Low: 36<br />
<br />
<a href="http://us.rd.yahoo.com/dailynews/rss/weather/Viacha__BL/*http://weather.yahoo.com/forecast/BLXX0018_f.html">Full Forecast at Yahoo! Weather</a><BR/><BR/>
(provided by <a href="http://www.weather.com" >The Weather Channel</a>)<br/>
]]></description>
<yweather:forecast
xmlns:yweather="http://xml.weather.yahoo.com/ns/rss/1.0"
code="11" date="24 Apr 2012" day="Tue" high="54"
low="38" text="Showers"/>
<yweather:forecast
xmlns:yweather="http://xml.weather.yahoo.com/ns/rss/1.0"
code="39" date="25 Apr 2012" day="Wed" high="59"
low="36" text="AM Showers"/>
<guid isPermaLink="false">BLXX0018_2012_04_25_7_00_BOT</guid>
</item>
</channel>
</results>
</query>