Scott Hanselman has already done a good job of covering it, but if you do any sort of web development, you know it can be a pain in the butt to download, install, and configure all of the necessary components (Visual Studio 2008, SQL Server 2008, IIS, etc).  The new Web Platform Installer is an awesome tool that downloads and installs everything for you.  From the site:

Overview

The Web Platform Installer (Web PI) is a simple tool that installs Microsoft's entire Web Platform, including IIS, Visual Web Developer 2008 Express Edition, SQL Server 2008 Express Edition and the .NET Framework. Using the Web Platform Installer’s user interface, you can choose to install either specific products or the entire Microsoft Web Platform onto your computer. The Web PI also helps keep your products up to date by always offering the latest additions to the Web Platform.

New Updates! Now supporting Windows XP and Windows Server 2003, Web PI makes it easy to install and stay up-to-date with the Microsoft Web Platform. This updated release lets you install ASP.NET MVC, Visual Studio Tools for Silverlight, and much more!

System requirements
  • Supported Operating Systems are: Windows Vista RTM, Windows Vista SP1, Windows XP, Windows Server 2003, Windows Server 2008
  • You must have administrator privileges on your computer to run Web Platform Installer
  • .NET 2.0 Framework
  • Supported Architectures: x86 and 64-bit

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I am going to try to teach myself web development in my copious spare time, so this installer is a really nice way to get all of the prerequisite software up and running.

Get it here: http://www.microsoft.com/web/channel/products/WebPlatformInstaller.aspx