Microsoft has published the actual featureset matrix and component/modules that will be included in each edition of Windows Vista & Longhorn Server.
Windows Vista Starter and Home Editions
– are targeted at home and personal users who do not have the need to perform application or web development. IIS 7 Web Server and FTP Server features are not available on these editions. However, if you look closely you will notice specific components of IIS 7 that can be installed on these Editions.
Windows Vista Home Premium Edition
– is the version to support the needs of the casual or hobbyist web developers; as such the majority of the IIS 7 Web Server features required for web site development are available. Features not normally associated with hobbyist web development such as FTP server, advanced Web authentication and authorization, and remote administration are not available on the Vista Home Premium Edition. Simultaneous connection limit is 3.
Windows Vista Professional Editions
– is targeted the professional web developer and provides professional web developers everything necessary to design, develop, and test web applications. (Professional Editions include Vista Business, Enterprise, and Ultimate Editions.) All of the IIS 7 features available on Windows Server Longhorn are available on the Professional Editions with the exception of remote administration. Simultaneous connection limit is 10.
Windows Server Longhorn Editions
– is ofcourse ready for full deployment of web applications: All features, including remote administration are available. Simultaneous connection limit is none.
Read more at source.