How loop through Databound DataTemplated ListBoxItems that are NOT Selected in wpf?

I can loop through selected items using "SelectedItems.Count" & "SelectedItems(i)".
I can loop through all items using "Items.Count" & "Items(i)".
How is one supposed to loop through non selected items given a ListBox with randomly selected items?
In VB6 I would loop through all Items and test using "If Not Selected(i) Then..."
In wpf there doesn't appear to be a "Selected" or "IsSelected" property! Am I missing something?

...

(I'm guessing I need to set "IsSelectedProperty" in the data template somehow, but do I? and how?)

Gouranga Gupta :-)