你要的应该是这个方法吧:
有英文耐心读一下
// Display a list of selected indices.
// The SelectedIndices property returns a SelectedIndexCollection
// object. Use its CopyTo method to copy the items to
// an array, so you can bind the list to a ListBox control.
int[] aIndices = new int[lstMultiSelect.SelectedIndices.Count];//lstMultiSelect为listbox
lstMultiSelect.SelectedIndices.CopyTo(aIndices, 0);
lstSelected.DataSource = aIndices;//lstSelected要显示的listbox