It's very simple example. but...
using System;
using System.Collections.Generic;
using System.Windows.Forms;

static class Program
{
/// <summary>
/// The main entry point for the application.
/// </summary>
[STAThread]
static void Main()
{
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
Application.Run(new Form1());//here!!!!!!
TestURL T = new TestURL();
T.download();
}
}

using System;
class TestURL
{

public void download()
{
CSDownloadURL web = new CSDownloadURL();
string strOut;
web.setURL1("http://www.google.com");
web.DownloadURL(out strOut);
Console.WriteLine(strOut);
}
}

using System;
using System.Text;
using System.IO;
using System.Net;

public class CSDownloadURL
{
private string m_strURL;
public void setURL1(string strURL)
{
m_strURL = strURL;
}

public void DownloadURL(out string strContents)
{
WebRequest req = WebRequest.Create(m_strURL);
WebResponse res = req.GetResponse();
int iTotalBuff = 0;
Byte[] Buffer = new Byte[128];
Stream stream = res.GetResponseStream();
iTotalBuff = stream.Read(Buffer, 0, 128);
StringBuilder strRes = new StringBuilder("");
while (iTotalBuff != 0)
{
strRes.Append(Encoding.ASCII.GetString(Buffer, 0, iTotalBuff));
iTotalBuff = stream.Read(Buffer, 0, 128);
}
strContents = strRes.ToString();
}
}

Thanks for your help