Openlayers Track example doesn't works

I try to make an example of Openlayers Track but it doesn’t works. I followed the example of this link:

And that’s my code:

var lgpx = new OpenLayers.Layer.Vector("Vallter_Nuria_8_2011", {
	strategies: [new OpenLayers.Strategy.Fixed()],
	protocol: new OpenLayers.Protocol.HTTP({
		url: "",  //I don't now what's the path. That tarck in the OSM Server.
		format: new OpenLayers.Format.GPX()
	style: {strokeColor: "green", strokeWidth: 5, strokeOpacity: 0.5},
	projection: new OpenLayers.Projection("EPSG:4326")

Thanks everybody!!