c# e SQl ajudae

 public partial class FrmLogin : Form
    {
        private OleDbConnection conexao;
        private OleDbCommand comando;

        public FrmLogin()
        {
            InitializeComponent();
            String str = @"Provider=Microsoft.Jet.OLEDB.4.0;Data Source=´C:\Documents and Settings\Administrador\Desktop\Hospital.mdb´";

            this.conexao = new OleDbConnection(str);
            this.comando = new OleDbCommand();

            this.comando.Connection = this.conexao;
            FrmPesquisaAdministrador frm = new FrmPesquisaAdministrador();
        }

        private void FrmLogin_Load(object sender, EventArgs e)
        {                
        }

        private void button1_Click(object sender, EventArgs e)
        {
            String Login = this.txtLogin.Text;
            String pw = this.txtSenha.Text;
            String lg = " SELECT usario FROM Usuarios WHERE usuario = ´ "+ Login +"´ ";
     
            OleDbCommand cmd = new OleDbCommand();
            cmd.Connection = this.conexao;
            cmd.CommandText = lg;

            this.conexao.Open();

            OleDbDataReader rd = cmd.ExecuteReader;
            if (rd.Read())
                {   
                     //Coloque sua lógica de login aqui.
                }
                else
                {
                   //Login Falhou
                }

            this.conexao.Close();
       }
    }

if (rd.Read())
{
     if (rd["ADMIN"] == "S")
     {
          //Abra seu form de admin
     }
     else
     {
         //Abra o outro form
     }
}
else
{
    MessageBox.Show("login inexistente");
}