After downloading simply type in the following commands:
1. Go to a Linux shell and login as the system administrator root:
2. Extract the downloaded archive file to /opt:
tar xvfz xampp-linux-1.6.6.tar.gz -C /opt

Warning: Please use only this command to install XAMPP. DON'T use any Microsoft Windows tools to extract the archive, it won't work.

Warning 2: already installed XAMPP versions get overwritten by this command.


That's all. XAMPP is now installed below the /opt/lampp directory.
To start XAMPP simply call this command:

/opt/lampp/lampp start

You should now see something like this on your screen:
Starting XAMPP 1.6.6...
LAMPP: Starting Apache...
LAMPP: Starting MySQL...
LAMPP started.
Ready. Apache and MySQL are running.
http://localhost

A matter of security (A MUST READ!)

As mentioned before, XAMPP is not meant for production use but only for developers in a development environment. The way XAMPP is configured is to be open as possible and allowing the developer anything he/she wants. For development environments this is great but in a production environment it could be fatal.
Here a list of missing security in XAMPP:

1. The MySQL administrator (root) has no password.
2. The MySQL daemon is accessible via network.
3. ProFTPD uses the password "lampp" for user "nobody".
4. PhpMyAdmin is accessible via network.
5. Examples are accessible via network.
6. MySQL and Apache running under the same user (nobody).

To fix most of the security weaknesses simply call the following command:
/opt/lampp/lampp security

It starts a small security check and makes your XAMPP installation more secure.