http://www.autodesk.com/myfirstautocadplugin My First Plug-in is a self-paced tutorial guide for a smooth introduction to the programming world. This is a “one-stop shop” learning path for users who know Autodesk products but are absolutely new to programming and are thinking about taking the plunge. In this guide, you will be working with the AutoCAD .NET Application Programming Interface (API) and the Visual Basic .NET programming language to create a ‘plug-in’ — a module that loads into AutoCAD to extend its functionality. Once you have finished this tutorial, you will understand the basics of .NET programming and how they are applied to AutoCAD.
Source: Autodesk
