Sorry i hit the wrong button. Anyway go to
http://www.weather.com/ and look at the top of the page.
Click on world, in the enter location box enter your location (ex.New York, Florida, ect.) and click go.
You will see a list of cities and states, click on yours.
On the next page in the address barr (http://) you will notice through the text a line that says USNY0996 (if your in New York like me).
Now ftp into your xbox and open your XboxMediaCenter.xml file and look all the way to the bottom and you will see this.
<weather>
<areacode>UKXX0085</areacode> <--enter the # from weather.com
<unitT>C</unitT> <--c for celsius, f for far fahrenheit
<unitS>K</unitS> <--k for kilometers, m for miles
<refresh>20</refresh>
</weather>
Save then open XBMC and click weather and your set.
Hope this helps