displaying column depends on dropdown's selection of another column in sharepoint form

public  void PopulateCompanyDropDown()
        {
            SPSite Site = new SPSite("http://xss-422:8000/default.aspx");
            SPWeb web = Site.OpenWeb();
            SPList SourceList1 = web.Lists["Company"];

            this.ddCompany.DataSource = SourceList1.Items.GetDataTable();
            this.ddCompany.DataTextField = "Title";
            this.ddCompany.DataValueField = "ID";
            this.ddCompany.DataBind();


        }
        public  void PopulateDepartmentDropDown()
        {
            SPSite Site = new SPSite("http://xss-422:8000/default.aspx");
            SPWeb Web = Site.OpenWeb();

            SPList SourceList2 = Web.Lists["Department Name"];

            //foreach (SPListItem item in SourceList2.Items)
            //{

            //    Console.WriteLine(item.Title.ToString());
            //    Console.WriteLine(item.Fields[9].ToString());
            //}


            string caml = "<Where>" +

                      "<Eq>" +
                          "<FieldRef Name='{0}'/>" +
                          "<Value Type=\"Lookup\">{1}</Value>" +
                      "</Eq>" +

                  "</Where>";

            SPQuery query = new SPQuery();
            string CompanyName = ddCompany.SelectedItem.Text.ToString();
            query.Query = string.Format(caml, "Company_x0020_Name", CompanyName);

            SPListItemCollection results = SourceList2.GetItems(query);

            this.ddDepartment.DataSource = results.GetDataTable();
            this.ddDepartment.DataTextField = "Title";
            this.ddDepartment.DataValueField = "ID";
            this.ddDepartment.DataBind();

            //txtManager.Text = SourceList2.Items[2]["Manager"].ToString();
            //txtUserName.Text = SourceList2.Items[2]["UserName"].ToString();
            //txtAddress.Text = SourceList2.Items[2]["UserComment"].ToString();

            //DataTable dtttt = results.
            //txtAddress.Text = SourceList2.Fields["UserComment"].ToString();

            DataTable dtttt = results.GetDataTable();

        }

  protected void ddCompany_SelectedIndexChanged(object sender, EventArgs e)
        {

            PopulateDepartmentDropDown();


        }