อยากทราบว่า จะเขียนcodeให้ Zip Folder เป็น.7zip บน vb2008 เขียนยังไงครับ ใครทราบช่วยบอกหน่อยครับ

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.IO;
using System.IO.Compression;
using System.Windows.Forms;

namespace Zipping
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void btnBrowse_Click(object sender, EventArgs e)
        {
            // Show the dialog where the user chooses the file to compress 
            if (openFile.ShowDialog() == DialogResult.OK)
            {
                txtPath.Text = openFile.FileName;
            }
        }

        private void btnCompress_Click(object sender, EventArgs e)
        {
// If the user has selected a path where to put the compressed file
if (saveFile.ShowDialog() == DialogResult.OK)
{
    // Bytes array in which we're going to store the actual file to be compressed
    byte[] bufferWrite;
    // Will open the file to be compressed
    FileStream fsSource;
    // Will write the new zip file
    FileStream fsDest;
    GZipStream gzCompressed;
    fsSource = new FileStream(txtPath.Text, FileMode.Open, FileAccess.Read, FileShare.Read);
    // Set the buffer size to the size of the file
    bufferWrite = new byte[fsSource.Length];
    // Read the data from the stream into the buffer
    fsSource.Read(bufferWrite, 0, bufferWrite.Length);
    // Open the FileStream to write to
    fsDest = new FileStream(saveFile.FileName, FileMode.OpenOrCreate, FileAccess.Write);

    // Will hold the compressed stream created from the destination stream
    gzCompressed = new GZipStream(fsDest, CompressionMode.Compress, true);

    // Write the compressed stream from the bytes array to a file
    gzCompressed.Write(bufferWrite, 0, bufferWrite.Length);

    // Close the streams
    fsSource.Close();
    gzCompressed.Close();
    fsDest.Close();
}
        }
    }
}