http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpref/html/frlrfsystemwindowsformscomboboxclassitemstopic.asp

NET Framework Class Library

ComboBox.Items Property

[C#]
public ComboBox.ObjectCollection Items {get;}


Items属性本身是ComboBox.ObjectCollection类型


http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpref/html/frlrfsystemwindowsformscomboboxobjectcollectionclasstopic.asp

.NET Framework Class Library

ComboBox.ObjectCollection Class


[C#]
public class ComboBox.ObjectCollection : IList, ICollection,
IEnumerable


Remarks
The System.Windows.Forms.ComboBox.ObjectCollection class encapsulates the items in the ComboBox. The object collection of a combo box can be used to manage many types of objects, including strings, images, and custom business objects.


也就是说，你可以在里面存放任何的数据类型

但是通过Items属性得到的，是你存入的实际对象，可以是string，也可以是别的

至于界面上显示成什么文字，估计就是数据对象的ToString()结果，我没有继续看了，你可以写程序测试一下