C#

private void Form1_Load(object sender, System.EventArgs e)
{
    //This is vital - tells the picturebox to accept dragdrop notifications
    //For some reason it does not seem to appear in intellisense or the Visual Studio designer.
    //It does build though!!
    this.pictureBox1.AllowDrop = true;
}

private void pictureBox1_DragEnter(object sender, System.Windows.Forms.DragEventArgs e)
{
    //Make sure item being dropped is a file
    if (e.Data.GetDataPresent(DataFormats.FileDrop))
    {
        e.Effect = DragDropEffects.All;
    }
    else//Otherwise do not allow drop
    {
        e.Effect = DragDropEffects.None;
    }
}

private void pictureBox1_DragDrop(object sender, System.Windows.Forms.DragEventArgs e)
{
    //Get an array of strings - needs an array because the user can drag more than one item
    //into the picturebox
    string[] itemsInDrop = (string[])e.Data.GetData("FileDrop", false);

    //loop over the strings
    foreach (string path in itemsInDrop)
    {
        //Do what you want here.
        //I check the iamge exists then try to load it into the picturebox.
        //This is obviously a bit pointless for more than one image, but acts as an example.
        //NB System.ArgumentException is thrown when you try to instantiate a bitmap object
        //with an invalid file path.
        FileInfo CheckForImage = new FileInfo(path);

        if(!CheckForImage.Exists)
        {return;}

        try
        {
            Bitmap newImage = new Bitmap(path);
            this.pictureBox1.Image = newImage;
        }
        catch(System.ArgumentException)
        {
            MessageBox.Show("The file at " + path + " is not a valid image.", "Invalid Image", MessageBoxButtons.OK, MessageBoxIcon.Error);
        }
    }
}

[DllImport("Netapi32")]
private static extern int NetServerEnum(
    string servername, //must be null
    int level, //101
    out IntPtr buffer,
    int maxlen, //out
    out int entriesread, //out
    out int totalentries, //out
    int servertype, //in 3 = all
    string domain, //null primary
    int resumehandle); //must be 0


[DllImport("Netapi32")]
private static extern int NetApiBufferFree(IntPtr ptr);


[StructLayout(LayoutKind.Sequential)]
internal class ServerInfo 
{
    public int platformid;
    [MarshalAs(UnmanagedType.LPWStr)]
    public string name;
    public int majorver;
    public int minorver;
    public int type;
    [MarshalAs(UnmanagedType.LPWStr)]
    public string comment;
}


class MachineConvertor : TypeConverter 
{
    public override StandardValuesCollection GetStandardValues(ITypeDescriptorContext context)
    {
      int eread, etot;
      IntPtr buffer;
      int l = 200;     
      int size = Marshal.SizeOf(typeof(ServerInfo));
      int res = NetServerEnum(
          null, 
          101, 
          out buffer, 
          size * l, 
          out eread, 
          out etot, 
          3, 
          null, 
          0);

      IntPtr p = buffer;
      ArrayList arr = new ArrayList(etot);
      for (int i = 0; i < eread; i++)
      {
          ServerInfo si = Marshal.PtrToStructure(p, typeof(ServerInfo)) as ServerInfo;   
          if (si.majorver > 4 && si.name != "")
            arr.Add(si.name);
          p = (IntPtr)((int)p + size);
      }

      res = NetApiBufferFree(buffer);
      return new StandardValuesCollection(arr);
    }


    public override bool GetStandardValuesSupported(ITypeDescriptorContext context)
    {
      return true;
    }
}