Architecture of MOSS:

Office Sharepoint Server: This layer manages excel services, infopath forms services, project server, enterprise search, policy, single sign on, business data catalogs.

Asp.Net Forms: This layer lies beneath Office Sharepoint Server layer. It is the layer responsible for Asp.Net based sites.

Windows Sharepoint Services: This is a collection of windows services which is used by sharepoint to connect to the database and can be used for development purposes.

Development tools: On the left is the collection of various development paradigms that can be used to perform development and create various webparts, or read and get information from WSS using Visual studio.