Another question is how can i make an operational layer visible by default when the flex viewer app is started?
<layer label="Streets" type="tiled" visible="true" url="http://server.arcgisonline.com/ArcGIS/rest/services/World_Street_Map/MapServer"/>
<layer label="test image Service" type="image" visible="false" url="http://cuo.geomatics.uct.ac.za/ArcGIS/rest/services/Capetown/ImageServer"/>