Mvc 3 Pre-select Html.DropDownListFor Not Working In Nerd Dinner?

Learning about dropdown lists, Im trying to add a RSVP create page for nerddinner as in Scott Gu's blog with a Html.DropDownListFor listing available dinners. I can get the dropdown list populated but I cannot get the dropdown to pre select the value ("Sample Dinner 2") I want. Im using an initilizer to seed a few dinner objects in the db. The database is sql ce 4 using a EF 'code first approach'. Sorry I know this is a v common problem and hate to ask, but honestly have spent quite some time on this but cant get it to work:

ViewModel

public class RSVPViewModel
{
public SelectList DinnersList { get; set; }
public RSVP Rsvp { get; set; }
public string SelectedItem { get; set; }
}
[code]...

So is not preselecting the dropdownlist with the value "Sample Dinner 2" when the page loads. The list displays ok and sets the correct DinnerID when I make a selection and click Submit.Tries this also:

@Html.DropDownListFor(x => x.SelectedItem, Model.DinnersList)

but doesnt set or bind to Rsvp.DinnerID.This preselects from the list but doesnt bind (or set Rsvp.DinnerID)

@Html.DropDownList("DinnersList")

I want to keep it mvc3 so want to implement with strong type using ViewModel approach (no ViewData) and preferably using Html.DropDownListFor (not Html.DropDownList).Viewbag seems unnecessary for this case.Thinking I should be using a selectList of selectListItems I tried this verbose approach :

RSVP rsvp = new RSVP();
string selected = "2";
List<SelectListItem> dinners = new List<SelectListItem>();

foreach (Dinner dinner in dbc.Dinners.ToList())
{
SelectListItem slDinner = new SelectListItem();
slDinner.Value = dinner.DinnerID.ToString();
slDinner.Text = dinner.Title;
slDinner.Selected = (slDinner.Value == selected);
dinners.Add(slDinner);
}
var dinnersList = new SelectList(dinners, "Value", "Text", selected);
var viewModel = new RSVPViewModel { DinnersList = dinnersList, Rsvp = rsvp, SelectedItem = selected };

However still no work. Should I be making use of the ViewModel SelectedItem property in: @Html.DropDownListFor.. somehow? Something like :@Html.DropDownListFor(x => x.SelectedItem, Model.DinnersList)but how to I get a selected value to set Rsvp.DinnerID. I think thats called binding.