The Microsoft Web Platform Installer is now v1.0. Simply putting, it provides you a single installer download of the web platform which includes IIS 7/116, Visual Web Developer Development Tool, SQL Server 2008 Express as well as the .NET Framework.
So, if you are running Windows XP, Windows Vista or Windows Server 2003/2008, it gives you all the stuff you require to start with web development.
Combined with this, the Web Application Installer which provides a lot of popular web applications such as the DotNetNuke, Graffiti etc., the Web Platform Installer is a great resource for starting your web development in Microsoft Platform. Some of these also support open source and shared source development and even require installation of PHP framework.
If you are a startup web company, all you would require to begin web development would be one of the above operating systems.
To install the Web Platform visithttp://www.microsoft.com/web/channel/products/WebPlatformInstaller.aspx
To install the Web Application Installer visithttp://www.microsoft.com/web/channel/products/WebApplicationInstaller.aspx
For more information, walk through and forums, visithttp://www.microsoft.com/web/channel/products/downloads.aspx