silverlight and database.

Question

I know this isn't a silverlight forum but I didn't see a specific one direct to it so hope this is ok spot.
Just learning silverlight and it seems talking to database is very different than what I am use to. I have researched and researched and I just don't seem to be doing it right.

What I am trying to do is read my forums user tables and match that when they log in my control it will know if they are a registered member or need to register at the forums.

I have done this with exact same database code in desktop application and it works fine but I can't get it done with silverlight.

I know have to do it in wcf which I also have not used before and here is some samples of what I have done to try it out.

In my xaml class.

 ServiceReference1.Service1Client logIn = new ServiceReference1.Service1Client();
                logIn.SaltReturnCompleted += new EventHandler<SaltReturnCompletedEventArgs>
(logIn_SaltReturnCompleted);
                logIn.SaltReturnAsync(tBoxUName.Text);

        private void logIn_SaltReturnCompleted(object sender, SaltReturnCompletedEventArgs e)
        {
            //this.salt = (string)e.Result;
            tBlockError.Text = (string)e.Result;
            tBlockError.Visibility = Visibility.Visible;
        }

In my web config.

 <connectionStrings>
    <add name="DBConnectionString" connectionString="Data Source=adress to server withheld for security;
Initial Catalog=database name withheld for security;Username=withheld for security;Password=withheld for security"/>
  </connectionStrings>

My wcf code.

  [OperationContract]
        public string SaltReturn(string tempUser)
        {
            string tempSalt = "";
            ArrayList salt = new ArrayList();
            using (SqlConnection con = new SqlConnection())
            {
                // Configure the SqlConnection object's connection string.
                con.ConnectionString = 
System.Configuration.ConfigurationManager.ConnectionStrings["DBConnectionString"].ConnectionString;

                // Open the database connection.
                try
                {
                    con.Open();
                }//closes try.
                catch (Exception)
                {
                }//closes catch.
                if (con.State == ConnectionState.Open)
                {
                    try
                    {
                        SqlCommand command = new SqlCommand
("SELECT salt FROM bvtvweb_user WHERE (username = '" + tempUser + "');", con);
                        SqlDataReader reader = command.ExecuteReader();
                        while (reader.Read())
                        {
                            tempSalt = reader.GetString(0);
                            salt.Add(tempSalt);
                        }//closes while.
                        reader.Close();
                    }//closes try.
                    catch (Exception)
                    {
                    }//closes catch.
                    if (salt.Contains(tempSalt))
                    {
                    }//closes if.
                    else
                    {
                        tempSalt = "";
                    }//closes else.
                }//closes if.
            }//closes using.

            return tempSalt;
        }//closes method.

    Can someone please clue me in on where I am going wrong?