protected void Button1_Click(object sender, EventArgs e)
    {
        string username = Request["username"].ToString();
        string password = Request["password"].ToString();
        OleDbConnection conn = new OleDbConnection();
        conn.ConnectionString = "Provider=Microsoft.Jet.OLEDB.4.0; Data Source=" + Server.MapPath("../web.mdb");
        conn.Open();


        string sql = "insert into  admin(username,password) values('"+username+"','"+password+"')";
        OleDbCommand comm=new OleDbCommand(sql,conn);
        comm.ExecuteNonQuery();
        Response.Write("<script language=javascript>window.alert('添加成功！');window.location.href='user_add.aspx';</script>");
        conn.Close();   

    }

想实现添加的功能可是
在comm.executenoquer那就停了下来!

这些都是最基本的操作。  
  自己多看看书和资料吧 ...
    注意方法的重载.