By default, the zoom level slider is oriented vertically. You can orient the slider horizontally by setting the height property of the slider to be null.
esriConfig.defaults.map.slider = { right:"10px", bottom:"10px", width:"200px", height:null };
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
<meta http-equiv="X-UA-Compatible" content="IE=7" />
<title>Map Slider Position and Height</title>
<link rel="stylesheet" type="text/css" href="http://serverapi.arcgisonline.com/jsapi/arcgis/1.5/js/dojo/dijit/themes/tundra/tundra.css">
<script type="text/javascript" src="http://serverapi.arcgisonline.com/jsapi/arcgis/?v=1.5"></script>
<script type="text/javascript">
dojo.require("esri.map");
function init() {
//configure map slider to be horizontally place at bottom right
esriConfig.defaults.map.slider = { right:"10px", bottom:"10px", width:"200px", height:null };
var map = new esri.Map("map", {
nav:false
});
map.addLayer(new esri.layers.ArcGISTiledMapServiceLayer("http://server.arcgisonline.com/arcgis/rest/services/ESRI_StreetMap_World_2D/MapServer"));
}
dojo.addOnLoad(init);
</script>
</head>
<body class="tundra">
Configure map slider's orientation
<div id="map" style="width:500px; height:500px; border:1px solid #000;"></div>
</body>
</html>