Some folks found that even when they only check Visual C++ in the setup options and uncheck Web Development tools, they still get Microsoft Visual Studio Web Authoring Component installed as a prerequisite right after .NET Framework 3.5. Why is this happening?
Historically in earlier versions of Visual Studio (2002-2005) it was always possible to add an HTML page and CSS file to the project, open and edit it in Design or Source view with intellisense and WYSISYG support. The designer didn't appear as a separate component because it consumed installed IE rendering engine (MSHTML.DLL) in VS 2002 and 2003 and had it's own engine (still based on IE) in VS 2005. Even if you only install C++ in VS 2005, you'll still see htmled.dll, csspkg.dll, vswebdesign*.dll and tridsn.dll installed. So VS 2008 is simply trying to keep functionality available to C++ developers. However, in VS 2008 designer is a separately installable component, so it's setup is visible as a separate entry and you'll get a separate entry in the Control Panel. See this earlier post for more details on the Web Authoring Component setup as well as this post for more information on the new HTML designer.