Declare @ud uniqueidentifier 
Select @ud = NEW_ID()
Insert into TableName (field) values ( @ud) 

Declare @ID int -- bigint
Insert into TableName (f1, f2,...) values ( @f1, @f2, ...) 
Select @ID = SCOPE_IDENTITY() -- @@IDENTITY 
Select ud from TableName  Where Field_with_IDENTITY = @ID 

using System;
using System.Windows.Forms;
using System.Data;
using System.Data.SqlClient; 

namespace WindowsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            string connetionString = null;
            SqlConnection sqlCnn ;
            SqlCommand sqlCmd ;
            SqlDataAdapter adapter = new SqlDataAdapter();
            DataSet ds = new DataSet();
            int i = 0;
            string sql = null;

            connetionString = "Data Source=ServerName;Initial Catalog=DatabaseName;User ID=UserName;Password=Password";
            sql = "Select * from product";

            sqlCnn = new SqlConnection(connetionString);
            try
            {
                sqlCnn.Open();
                sqlCmd = new SqlCommand(sql, sqlCnn);
                adapter.SelectCommand = sqlCmd;
                adapter.Fill(ds);
                for (i = 0; i <= ds.Tables[0].Rows.Count - 1; i++)
                {
                    MessageBox.Show(ds.Tables[0].Rows[i].ItemArray[0] + " -- " + ds.Tables[0].Rows[i].ItemArray[1]);
                }
                adapter.Dispose();
                sqlCmd.Dispose();
                sqlCnn.Close();
            }
            catch (Exception ex)
            {
                MessageBox.Show("Can not open connection ! ");
            }
        }
    }
}