KB100007: How to re-install ASP.NET on a Windows platform

If you want to run ASP.NET web applications on your local computer, you must have both Internet Information Services (IIS) and ASP.NET installed. IIS is necessary for providing web service and ASP.NET is necessary for providing handling of the family of ASP.NET web applications (ASPX, ASMX, etc). IIS is installed by default for installations of Windows 2000 and Windows XP. ASP.NET is installed by default during .NET Framework installation. However, if you attempt to install the .NET Framework on a Windows 2000 or Windows XP machine that doesn't have IIS installed, the .NET Framework installation will detect that IIS is not available and thus will not install ASP.NET component of the framework. If you subsequently install IIS at a later time, you will have to install ASP.NET manually.