Lets this tutorial be simple for the same I am trying to tell you to install it in localhost. Which is Simple as of now
1. Download & Install
You can grab your copy of CodeIgniter from the downloads section of CodeIgniter Official Website i.e Download CodeIgniter
The Latest Version when I was documenting this Tutorial was 1.7.2
Once after downloading the CodeIgniter extract the files to the machine. You will see a folder with System , User guide, License, and index page.
Inside User guide folder if you run index page, You will be shown the Nice Documentation of CodeIgniter, I believe it is the Best source to learn, but this tutorial the better than the best 
Next, If you have XAMPP already installed in then copy the index, license and System Folder to your htdocs and project specific folder.
You are almost done with the installation of CodeIgniter.
Do not wonder , Code Igniter is that Simple to Install .
