problems in sending email using free smtp server in asp.net

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ASP.NET

Hi, i am yogesh and i have a problem in sending email using free smtp server.
I have windows 7 prof...(os).
windows7 has not haveing default smtp server installed... so what i have to do please
give me example of step by step installing smtp server as i have tried many options
i also used gmail server but failed. I also found that windows 7 no longer support
smtp server so what to do... my code i just tried using gmail server is as follows..

string from = "imyogesh@mail.com"; // this is my gmail account
              string to = "imyogesh@mail.com";

System.Net.Mail.MailMessage mail = new System.Net.Mail.MailMessage();
 mail.To.Add(to);
 mail.From = new MailAddress(from, "One Ghost" , System.Text.Encoding.UTF8);
mail.Subject = "This is a test mail" ;
mail.SubjectEncoding = System.Text.Encoding.UTF8;
mail.Body = "This is Email Body Text";
mail.BodyEncoding = System.Text.Encoding.UTF8;
mail.IsBodyHtml = true ;
mail.Priority = MailPriority.High;

SmtpClient client = new SmtpClient();
client.Credentials = new System.Net.NetworkCredential(from, "PASSWORD");

client.Port = 587; // Gmail works on this port
client.Host = "smtp.gmail.com";
client.EnableSsl = true; //Gmail works on Server Secured Layer
       try
        {
            client.Send(mail);
        }
        catch (Exception ex) 
        {
            Exception ex2 = ex;
            string errorMessage = string.Empty; 
            while (ex2 != null)
            {
                errorMessage += ex2.ToString();
                ex2 = ex2.InnerException;
            }
   HttpContext.Current.Response.Write(errorMessage );
        }  

what is wrong with this code.
i have installed iis7... and i don't know how to install smtp serve..
please help me i m trying since 5 day. i need to test my application for sending emails.
As windows 7 is not supporting smtp server what i have to do.
with this code iam getting error.

/*
System.Net.Mail.SmtpException: The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.5.1 Authentication Required. Learn more at at System.Net.Mail.MailCommand.CheckResponse(SmtpStatusCode statusCode, String response) at System.Net.Mail.MailCommand.Send(SmtpConnection conn, Byte[] command, String from) at System.Net.Mail.SmtpTransport.SendMail(MailAddress sender, MailAddressCollection recipients, String deliveryNotify, SmtpFailedRecipientException& exception) at System.Net.Mail.SmtpClient.Send(MailMessage message) at ADVANCED_FORUM.email.Page_Load(Object sender, EventArgs e) in D:\DOTNET\web\ADVANCED_FORUM\ADVANCED_FORUM\email.aspx.cs:line 84
*/

pleas suggest me solution....