If you want to develop or test ASP.NET application, IIS(Internet Information Server) is required, yet it may not come with your OS and you must configure it manually. Let me show the process on Windows 7 Enterprise edition.
1. Start -> Control Panel -> Programs and Features (Start -> run<appwiz.cpl>)
2. Click "Turn Windows features on or off"
3. Expand the "Internet Information Services" node, check required options, and then click "OK"
Now the IIS is configured on your computer, if you navigate to http://localhost/, you can see the default page,
and you can start the IIS manager by "Start -> Run<inetmgr>".