A typo in a link to the sample code caused the code to not appear in the topic How to: Use the Open File Dialog Box topic. Here's the C# and VB code you should have gotten with the Silverlight 2 Beta 1 SDK documentation.

C# code from the Page.xaml.cs file

using System;
using System.Collections.Generic;
using System.Linq;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;
using System.IO;
using System.Text;

namespace SL_OpenFileDialog_CS
{
    public partial class Page : UserControl
    {
        public Page()
        {
            InitializeComponent();
            bOpenFileDialog.MouseLeftButtonDown += new MouseButtonEventHandler(bOpenFileDialog_MouseLeftButtonDown);
        }

        void bOpenFileDialog_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
        {
            // Create open file dialog box
            OpenFileDialog openFileDialog1 = new OpenFileDialog();
            openFileDialog1.Filter = "Text Files (*.txt)|*.txt | All Files (*.*) | *.*";
            openFileDialog1.FilterIndex = 2;

            if (openFileDialog1.ShowDialog() == DialogResult.OK)
            {
                //Open the selected file to read.
                System.IO.Stream fileStream = openFileDialog1.SelectedFile.OpenRead();

                using (StreamReader reader = new StreamReader(fileStream))
                {
                    // Read the first line from the file and write it to the text box.
                    tbResults.Text = reader.ReadLine();
                }
                fileStream.Close();
            }

        }

    }
}

VB code from the Page.xaml.vb file

Partial Public Class Page
    Inherits UserControl
  
    Public Sub New()
        InitializeComponent()
        AddHandler bOpenFileDialog.MouseLeftButtonDown, AddressOf Me.bOpenFileDialog_MouseLeftButtonDown

    End Sub

    Private Sub bOpenFileDialog_MouseLeftButtonDown(ByVal sender As Object, ByVal e As MouseButtonEventArgs)
        ' Create open file dialog box
        Dim openFileDialog1 As OpenFileDialog = New OpenFileDialog
        openFileDialog1.Filter = "Text Files (*.txt)|*.txt | All Files (*.*) | *.*"
        openFileDialog1.FilterIndex = 1
        If (openFileDialog1.ShowDialog = DialogResult.OK) Then
            'Open the selected file to read.
            Dim fileStream As System.IO.Stream = openFileDialog1.SelectedFile.OpenRead
            Dim reader As System.IO.StreamReader = New System.IO.StreamReader(fileStream)
            ' Read the first line from the file and write it to the text box.
            tbResults.Text = reader.ReadLine
            fileStream.Close()
        End If

    End Sub
   
End Class