DirectoryObjectPickerDialog picker = new DirectoryObjectPickerDialog()
{
    AllowedObjectTypes = ObjectTypes.Users | ObjectTypes.Groups | ObjectTypes.Computers,
    DefaultObjectTypes = ObjectTypes.Computers,
    AllowedLocations = Locations.All,
    DefaultLocations = Locations.JoinedDomain,
    MultiSelect = true,
    ShowAdvancedView = true
};
using (picker)
{
    if (picker.ShowDialog() == DialogResult.OK)
    {
        foreach (var sel in picker.SelectedObjects)
        {
            Console.WriteLine(sel.Name);
        }
    }
}