How to select ListBox item by ValueMember

You can use the SelectedValue property of your list control:

Listbox1.SelectedValue = 345;

You must assign data via DataSource property of ListBox control, not via Items.Add. After that you can use ValueMember to select items:

listBox1.DataSource = GetPeople();
listBox1.DisplayMember = "Name";
listBox1.ValueMember = "Id";

// Now you can use
listbox1.SelectedValue = 345;

UPDATE: Items is a member of ListBox class, but SelectedValue is a ListControl property, which can use only DataSource.