Hibernate version:
released on 03/5/2007  1.2.0.GA 
My platform VS2005+SqlServer2005 express
i was following the guide on  
http://www.hibernate.org/362.html.
Error
 NHibernate.HibernateException: The dialect was not set. Set the property hibernate.dialect
Here is my steps...
1 create the database.
Code:
CREATE TABLE users (
  LogonID nvarchar(20) NOT NULL default '0',
  Name nvarchar(40) default NULL,
  Password nvarchar(20) default NULL,
  EmailAddress nvarchar(40) default NULL,
  LastLogon datetime default NULL,
  PRIMARY KEY  (LogonID)
)
go
2 I  create a Class library project in VS2005. 
Create the Class User. (The code is the same as the  tutorial)
3 add the User.hbm.xml in the class library.(the same path as the Class User)
here is the content.... 
Code:
<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2">
  <class name="NHibernate.Examples.QuickStart.User, NHibernate.Examples" table="users">
    <id name="Id" column="LogonId" type="String" length="20">
      <generator class="assigned" />
    </id>
    <property name="UserName" column="Name" type="String" length="40"/>
    <property name="Password" type="String" length="20"/>
    <property name="EmailAddress" type="String" length="40"/>
    <property name="LastLogon" type="DateTime"/>
  </class>
</hibernate-mapping>
I didnot make any change in this xml file.
4I changed  the Build Action to "Embeded Resourse" , and build the 
assembly named  NHibernate.Examples.5 I created a web project and added refference to NHibernate.dll  and the assambly I just created...
6 I created the app.config file in the Web Project as follows...
Code:
<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <configSections>
    <section
      name="nhibernate" 
      type="System.Configuration.NameValueSectionHandler, System, Version=1.0.5000.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" 
    />
  </configSections>
  <nhibernate>
    <add 
      key="hibernate.connection.provider"
      value="NHibernate.Connection.DriverConnectionProvider"
    />
    <add
      key="hibernate.dialect"
      value="NHibernate.Dialect.MsSql2000Dialect"
    />
    <add
      key="hibernate.connection.driver_class"
      value="NHibernate.Driver.SqlClientDriver"
    />
    <add
      key="hibernate.connection.connection_string"
      value="Data Source=NOTEBOOK\SQLEXPRESS;Initial Catalog=Nhibernate;Integrated Security=True"    
    />
  </nhibernate>
</configuration>
I only change the connectString according to my database.
7 I created a index.aspx and wrote the following code in Pade_Load event 
Code:
 Configuration cfg = new Configuration();
        cfg.AddAssembly("NHibernate.Examples");
        ISessionFactory factory = cfg.BuildSessionFactory();
        ISession session = factory.OpenSession();
        ITransaction transaction = session.BeginTransaction();
        User newUser = new User();
        newUser.Id = "joe_cool";
        newUser.UserName = "Joseph Cool";
        newUser.Password = "abc123";
        newUser.EmailAddress = "joe@cool.com";
        newUser.LastLogon = DateTime.Now;
        // Tell NHibernate that this object should be saved
        session.Save(newUser);
        // commit all of the changes to the DB and close the ISession
        transaction.Commit();
        session.Close();
        TextBox1.Text = "Succeed.....";
but When I run it ....The error message is
 NHibernate.HibernateException: The dialect was not set. Set the property hibernate.dialect.
and 
line 15:     {
line 16:         Configuration cfg = new Configuration();
line 17:         cfg.AddAssembly("NHibernate.Examples");
line 18:         ISessionFactory factory = cfg.BuildSessionFactory();
行 19:         ISession session = factory.OpenSession();