refering to this thread,

 

 http://www.dotshoppingcart.com/View/Forum/DotShoppingCart%20Forums/Support/Using%20DotShoppingCart/675.aspx

 

I did this code for radio button checked in when page is opened. 

 

public void AutoSelect()
    {
        base.DataBind();
        pnlEmpty.Visible = false;
        SiteConfigurationSection section = SiteConfigurationSection.GetSection();
        methods = ShippingService.GetShippingMethods(ShippingPackage.GetShippingPackage(Cart.Get(),
            (Address)Session["ShippingAddress"], section.LocationCountry, section.LocationState, section.LocationCity, section.LocationZipcode));
        rptShippingMethods.DataSource = methods;
        rptShippingMethods.DataBind();
        RadioButton rdoShiping = (RadioButton)rptShippingMethods.Items[0].FindControl("rdoShiping");
        rdoShiping.Checked = true;
        Session["ShippingMethod"] = methods[0];
       
    }