// Checking for mandatory fields
YAHOO.util.Event.onDOMReady( function(){
  var form = YAHOO.util.Dom.get( 'institution_search' );
  YAHOO.util.Event.addListener( form, 'submit',checkForm);
});

function checkForm(e)
{
      if ( this.searchProviderLocation.value == "" &&
           this.searchProviderName.value == "" &&
           this.searchProviderType.value == "" )
      {
        YAHOO.util.Event.stopEvent(e);
        alert("At least one option needs to be selected");
      }
}