Can you please post questions that are not directly related to this book in a more general ASP.NET category here: http://p2p.wrox.com/asp-net-asp-12/
? Makes it easier for others to join and learn from the discussion.
Anyway, you can differentiate types in different DBML files by setting the Entity Namespace property of the model (click the design surface and then press F4).
However, with only 15 tables, I would add them all to a single DBML file.
and then always use the same datacontext throughout the project.
The same datacontext *type*, not the actual instance. That is, you want to "new" up a context in each page, and not use a global one that all your pages use.