Visual Web Developer 2008 Express Edition is a free version of Visual Studio for building all kinds of web applications - you'll also get the free version of SQL Server 2008 from the same place.
Everything you need to get started building Silverlight 2 applications - including download links and information.
Codeplex.com is one of the open source repositories where you’ll find loads of ASP.NET and Silverlight projects – download code for your own use, contribute to existing projects or create your own. Microsoft contributes much of its open source to Codeplex.com including extensions to ASP.NET such as the model-view-controller support in ASP.NET MVC.
Code Chronicles: It's often easy to forget how much commonality there is between our coding worlds - and as programmers and designers we can get pretty passionate about the tools, languages and approaches we use to create software... and every one has its advantages and its quirks... take a look at Code Chronicles to see where you're favourite programming language comes from.
The Microsoft Web Platform site includes link to the Web Platform Installer which auto configures a machine for building and running web applications on Windows in ASP.NET or PHP.