How to physically separate tiers?

[Rupert]

I am developing a system in ASP.NET and am new to the technology.

I am running everything on the laptop I am developing on (windows xp).
The DB is Oracle and my aspx pages and C# code behind classes and
other classes are in one directory under IIS.

The client plans to have an application server and two web servers
(one for the intranet connections and one for internet connections).
For security reasons the web servers will not be able to access the DB
only the application server will. So there will be 4 physical tiers
- DB
- Application server (DB access and business logic?)
- Web servers (Presentation logic and business logic?)
- Browser clients (GUI)

I do not understand how to physically separate my aspx pages, C# code
behind classes and data access/business rule classes or even what my
options are. How do my classes/objects on the web servers communicate
with/instantiate objects on the application server? Should I have my
business rule classes and data access classes on the application
server or just the data access classes?

Could someone explain the usual practice and the choices I have or
point me to a URL that does a good job of explaining?

Thanks in advance,
Rupert

[Rupert]

My researching today has been more successful than yesterday. It would
appear that .NET remoting is what I should use. Since one of the web
servers (in the DMZ) will have to connect to the application server
through a firewall it would seem that binary over HTTP using IIS is
the way to go. (Although I still have not read up on the .NET
component services infrastructure)

The classes on the application server would provide data access and
would return number records affected, a DataReader or a DataSet (not
sure how this would effect using a dataset to update the DB via a
DataAdaptor).

Am I on the right track?
Rupert