There are a lot of tutorials on the internet instructing how to make N-tier applications.
Link posted by BestJewSinceJC is a good reference to learn and develop ASP.NET MVC (MVC2) framework. If you have no experience and you want to learn something new then I say give the technology a try.
If you want to implement 3-tier architecture in your ASP.NET Web-form application then it is a three-part breakdown — presentation, business logic (business access layer), and data (data access layer). Here is a good tutorial - N-Layered Web Applications with ASP.NET 3.5 Part 1: General Introduction.
Thank You very much
your links are really very helpful for me..
thanking you once again