I have created a custom property and a silverlight component to present one in edit and view mode :

public override void CreateEditControls() {

System.Web.UI.SilverlightControls.Silverlight sl = new System.Web.UI.SilverlightControls.Silverlight();

sl.Source = EPiServer.UriSupport.Combine(UriSupport.SiteUrl.ToString(), "ClientBin/DagensIndustri.SilverLightDemo.xap");

sl.ID = "VideoPlayerXAML";

sl.MinimumVersion = "2.0";

sl.ScaleMode = System.Web.UI.SilverlightControls.ScaleMode.None;

sl.Width = System.Web.UI.WebControls.Unit.Pixel(850);

sl.Height = System.Web.UI.WebControls.Unit.Pixel(400);

Controls.Add(new ScriptManager());

Controls.Add(sl);

}

 But I have an error when property should be displayed : "Script controls may not be registered before PreRender"

Does anybody have any sugestions?