Microsoft Windows Vista introduces the next generation operating system technology and software development platform that will be used by application developers and enterprises worldwide. As part of enhancing the security and user experience of Windows Vista, many new features have been introduced and existing features have been improved.

While Windows Vista is highly compatible with most of the applications written for Microsoft Windows XP, Microsoft Windows Server 2003, and their service packs, some amount of compatibility breaks are inevitable due to new innovations, security tightening, and increased reliability. For that reason, Microsoft is continuously striving to achieve the best possible compatibility solutions for existing applications running on Windows Vista.  This document is the first step for application developers to become familiar with how to verify the compatibility of their applications. The document also provides an overview of the few known application incompatibility issues in Windows Vista and provides links to detailed white papers and other developer guidance.

http://msdn.microsoft.com/windowsvista/default.aspx?pull=/library/en-us/dnlong/html/AppComp.asp#appcomp_topic24