My comments on Renaud Bompuis’s answer messed up.
Actually, you can use late binding, and the reference to the 11.0 object library is not required.
The following code will work without any references:
Dim f As Object
Set f = Application.FileDialog(3)
f.AllowMultiSelect = True
f.Show
MsgBox "file choosen = " & f.SelectedItems.Count
Note that the above works well in the runtime also.