Let me start from the beginning. Every web page is run on a server. These servers are all inter connected on the to each other by the World Wide Web. There are two primary types of servers. One is the Apache server. The other is IIS, or Internet Information Server. Apache is a free server that you can download at http://www.apache.org
This is an open source based server. It is used primarily on Linux and Unix OS's, but that is a totally other topic.
You said that you wanted to know about IIS. IIS was created by Windows. It was implemented in the Window NT 3.51 kernel(A Kernel is the core group of programs that make up an operating system). IIS was created as a network file and application server that would transmit information by using HTTP or the internet. For most people IIS is a means of getting a web page up and running without having to go through to many steps or know confusing codes or directories.
IIS comes as a standard or add on program for every Window OS from 95 through Vista and Server 2008. If you want to get and install IIS on an XP computer all that you have to do is input the CD into your drive and then click on Install optional Windows components. There will be a box that appears and you can then choose which apps you want to install. From here you click on the check box next to Internet Information Server(IIS), and any other components that you would like to install. Then you click on next and the install wizard does every thing else.
From here I am going to leave you on your own to do what all of us do when we want to know more about something we do some research and learn and use the service or product that we want to know about. I have given you the information on the basis of what IIS is and how to install it on an XP computer. It is up to you to go out and expand upon that knowledge.