.net - Show A Waitcursor While Waiting For A Combobox To Render?

I have a strange issue when binding a combobox in a WPF window.I am loading a List object, to populate the combobox, through it's .ItemsSource, on Window Load, however, it does not populate.At least, not until the arrow is clicked on. Once the arrow is clicked on, the window freezes up, and after a minute or so, the 4000+ records are displayed in it.Now, the list gets loaded, however, when I click on the combobox it takes awhile for it to render, so how can I show a waitcursor while it is rendering the list?Here's the Xaml for it:

<ComboBox Grid.Column="1"
HorizontalAlignment="Stretch" Margin="3" Name="tUser" VerticalAlignment="Stretch"
DisplayMemberPath="UsersName" SelectedValuePath="UserID" SelectedValue="0"/>

And the code-behind is:

Private Sub CreateTask_Loaded(sender As Object, e As System.Windows.RoutedEventArgs) Handles Me.Loaded
Using New WaitCursor
_LA.Show()
Me.tOrder.ItemsSource = GetOrderList()

[code]....