If SaveFD.ShowDialog() = DialogResult.OK Then
        Dim sb As New System.Text.StringBuilder()

        For Each o As Object In ListBox1.Items
            sb.AppendLine(o)
        Next

        System.IO.File.WriteAllText("c:\mypath\output.txt", sb.ToString())
    End If

Textbox1 write to a file :

1: My.Computer.FileSystem.WriteAllText("c:\value1.txt", TextBox1.Text, False)

2: Dim objWriter As New System.IO.StreamWriter("c:\value1.txt", False)

objWriter.WriteLine(Textbox1.Text)
objWriter.Close()