Error: the XML response that was returned from the server is invalid SOLUTION

If your page on localhost says:
Error: the XML response that was returned from the server is invalid.

The Solution Steps are :

1. Install without the sample data
2. Install sample data (...\yourjoomla\installation\sql\mysql\sample_data.sql) manually for example in phpmyadmin - navigate to your target database
3. Delete installation folder, then refresh frontend, now with the sample data installed

Additionally, turning off temporarily your php errors in php.ini might help to proceed with the installation.

1. Find your php.ini (root directory)
2. Search for this line in php.ini that says" error_reporting = E_ALL"
3. Uncomment then replace with this line "error_reporting = E_ALL & ~E_NOTICE"
4. Restore this setting as needed

Change/Remove Administrator Page Footer

On standard package installation, Joomla displays some description on their footer in administrator page.  In some versions, it says "Joomla is free software ...." and also display the version being used.
You can change/remove in some steps :

1. Go to
   - /administrator/templates/(name of template being used)/login.php 
   - /administrator/templates/(name of template being used)/cpanel.php
   - /administrator/templates/(name of template being used)/index.php
2. Open file and edit/remove the bottom code (on <div> footer </div>) then save it

* do it on each administrator templates

Change Favicon

You could change Joomla Favicon on following steps :

1. You must have favicon.ico
    - you can create it on : Favicon Generator
    - also, you could make it with component : "Favicon", but just can run on Joomla 2.5
       with this component also you could place it with one-click
2. Place favicon.ico on /templates folder (administrator and site templates)

PS : in some third-party template (ex : JA/JoomlArt), also you must place favicon.ico on main /images folder on root

Change Admin Login Logo (Lock)

If you wish to change padlock image on Joomla Administrator Page, you can change this with some steps :
1. Open Administrator directory
    Joomla 1.5 :
     /administrator/templates/(name of template being used)/images/j_login_lock.jpg    
    Joomla 1.7-2.5     
    /administrator/templates/(name of template being used)/images /j_login_lock.png
2. Open and edit the image with exact size and save on its place