checkArtistAvailability = function(artist_name, callback) {
    callback = dojo.lang.isFunction(callback) ? callback : artistAvailableSuccess;
    params = {
        url: MP3_BASE_URL + '/index.php?event=Response&type=Artist&action=artist_exists&artist_name=' + escape(artist_name),
        onSuccess: callback,
        onFailure: function() { alert('an error occurred'); }
    }
    dojo.io.basicXHRTransport(params);
}

artistAvailableSuccess = function(t, d) {
    MP3_DIALOG_WIDGET = dojo.widget.byId('ui-dialog');
    dojo.style.setOpacity(dojo.byId('ui-dialog'), 0);
    message = '<div style="width: 300px;"><div>'+d+'</div><div style="text-align: right;"><a href="javascript:void(0);" onclick="MP3_DIALOG_WIDGET.hide();">close</a></div></div>';
    MP3_DIALOG_WIDGET.displayHandler(message);
}