Marco in the original booked used what is called a provider model. Back in ASP.NET 2.0 this model was being pushed as the new way to program. Since then there has been a large push for a more separated data access model. Such as nHibernate or Entity Framework, where you create your domain objects (your BLL) and then use reflection, configuration, separation, and IoC to do all the DAL operations.
There is another book which deals with the beer house and Entity Framework called ASP.NET 3.5 Website Programming.
For our book we decided to update the model to something a little more modern, that was easy to use, and didn't step on the work that was being done in the other book. That is why we choose LINQ-to-SQL.
Also the DAL from the original book is an hand crafted ORM vs an ORM designed for mass consumption like LINQ-to-SQL. If you would like to learn more about MVC in a quick synopsis. Please check out my 7 part series on my blog, which is a preview release of Chapter 2 of my book.
That explains ASP.NET MVC in a quick and consise manor. But to answer your question about what a model is, you can start here:
A model is basically anything you can retreive and store some kind of data in. For smaller applications the model will be the DAL, or larger applications the model will be the BLL. Hope this answers you questions. Also your custom designed DAL that you have used on 30+ sites can still be your model in MVC, so all your work isn't lost. :)