codice:
 cosi come il tuo 
uno = picturebox1 due = picturebox2
ma non va .


Public Class Form1    
   Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load     
  End Sub      
     

    Private Sub uno_MouseDown(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles uno.MouseDown
       
  uno.DoDragDrop(uno.Image, DragDropEffects.All)  

    End Sub

      Private Sub due_DragDrop(ByVal sender As Object, ByVal e As System.Windows.Forms.DragEventArgs) Handles due.DragDrop  

       due.Image = e.Data.GetData(DataFormats.Bitmap)    
   End Sub   
      
  Private Sub due_DragEnter(ByVal sender As Object, ByVal e As System.Windows.Forms.DragEventArgs) Handles due.DragEnter   
      e.Effect = DragDropEffects.Copy    
 End Sub

 End Class