How To Connect To Sql Server As Other's Window Login Rather Than User's Window Login Thorugh ASP.NET.

Dear members,

In MSDN, it says that it is recommended to use windows authentication to connect to SQL Server rather than use mixed authentication.

I create user deltasqluser on windows OS, and I specify in my webform ASP.NET script below :

protected System.Web.UI.WebControls.Label Label1;
private string _connString = @"data source=deltasql2000;initial catalog=northwind;integrated security=false;user id=deltasqluser";
/*
comment : I login to my windows as deltakoronx, and I want to every user (including me), connected to sql server through IIS, will be identified as deltasqluser not as user's login (impersonate)
*/
private void Page_Load(object sender, System.EventArgs e)
{
SqlConnection conn = new SqlConnection(_connString);
SqlCommand cmd = new SqlCommand();
cmd.Connection = conn;
cmd.CommandType = CommandType.Text;
cmd.CommandText = "select suser_sname()";

conn.Open();


string userName = cmd.ExecuteScalar() as string;
conn.Close();
conn.Close();
Label1.Text = userName;
}


at web.config, I add :
<identity impersonate="false" userName="deltasqluser" password="" />


at IIS webApplication1's properties, tab "Directory Security", at "Authentication and access control" section, I checked "enable anonymous access" with user : DELTAIUSR_DELTA and checked "Integrated Windows Authentication",


at query analyzer, I login as "sa" and execute script below :
exec sp_grantdbaccess 'deltasqluser','northwind'


when I run the ASP.NET script, error at conn.Open(); with error message :
Login failed for user 'NT AUTHORITYNETWORK SERVICE'.


What should I do so that IIS login to SQL Server as user deltasqluser not as "NT AUTHORITYNETWORK SERVICE" ?

Regards,

Koronx