Now live on Technet (yes, that Technet -- they're part of the family now, so be nice).
This seven chapter article is intended to:

This paper provides guidelines for developing applications that use the directory and security services of the Microsoft® Windows® platform. Specifically, the paper discusses identity considerations and guidelines when developing Microsoft ASP.NET multi-tier intranet and extranet Web applications using Microsoft Visual Studio® .NET and Microsoft Windows Server™ 2003 directory and security services.

TTFN - Kent