Что такое библиотеки MSDN и зачем они нужны?

Microsoft Developer Network (MSDN) - это подразделение компании Microsoft, ответственное за взаимодействие фирмы с разработчиками. Но при упоминании MSDN на форумах чаще всего имеют в виду "MSDN Library" - обширную библиотеку документов по технологиям MS, либо "MSDN Subscription" - платную подписку на продукты MS, включая MSDN Library. MSDN Library обычно используется программистами.

http://msdn.microsoft.com/
http://msdn.microsoft.com/library/rus/
http://msdn2.microsoft.com/

Это технические описания API Windows с примерами, документацией и статьями. Нужны для написания программ для Windows (вернее для понимания работы системы) . Это все текстовая информация, а не библиотеки нужные для компиляции программ.

MSDN Library is a library of official technical documentation content intended for developers developing for Microsoft Windows. MSDN stands for the Microsoft Developer Network. The MSDN Library documents the APIs that ship with Microsoft products and also includes sample code, technical articles, and other programming information. It is available free on the web and on CDs and DVDs for paid MSDN subscribers. Initially, the disc version was only available as part of an MSDN subscription and was released on a quarterly basis (January, April, July and October). However, in recent times (2006 and later), it can be freely downloaded from the Microsoft Download Center in the form of ISO images and the CD/DVD releases are no longer published quarterly. Instead, its release schedule is now aligned with major software releases (major Visual Studio release, major Windows release or service packs).

Since May 2006, Microsoft has also started producing a community CD version of the MSDN Library freely available for download as ISO images on its Download Center which contains only updated content. The community distribution of the MSDN Library is aimed at developers in countries where broadband internet connections are not readily available.

Visual Studio Express editions integrate only with the MSDN Express Library which is a subset of the full MSDN Library, although either MSDN edition can be freely downloaded and installed standalone.

документация же