Drupal 7.13 and Services 3.5 XML Payload schema to Update Node?
See updated EDIT above.

RAW PAYLOAD:-

&lt;?xml version="1.0" encoding="UTF-8"?&gt;
&lt;data&gt;
    &lt;name&gt;user&lt;/name&gt;
    &lt;title&gt;Change this owner!&lt;/title&gt;
    &lt;body&gt;
        &lt;und is_array="true"&gt;
               &lt;item&gt;
                &lt;value&gt;Another owner test&lt;/value&gt;
            &lt;/item&gt;
        &lt;/und&gt;
    &lt;/body&gt;
&lt;/data&gt;