<script type="text/javascript">
var map, layer;
function init(){
map = new OpenLayers.Map( 'map' );
layer = new OpenLayers.Layer.WMS( "OpenLayers WMS",
"http://vmap0.tiles.osgeo.org/wms/vmap0",
{layers: 'basic'} );
map.addLayer(layer);
map.numZoomLevels =13;
map.zoomToMaxExtent();
map.addControl(new OpenLayers.Control.LayerSwitcher());
map.addControl(new OpenLayers.Control.ZoomPanel());
map.addControl(new OpenLayers.Control.PanZoomBar({'position':new OpenLayers.Pixel(50, 0), 'zoomStopHeight':5}));
}
</script>