In order to install windows, you need the Windows XP CD You need to make sure all of your computer hardware is setup and ready. After that put in the CD read the licensing agreement. If you have any important data on your computer you need to back it up before doing the installation or it will get deleted. You need to follow the directions it gives you as you go along in order for the installation to be done properly.
For a tutorial on how to install Windows XP click here.
For a video tutorial click here.