Note: I'm leaving this page as is for information purposes, but I don't recommend you follow this tutorial for installing Drush. I recommend using composer to install Drush.
Below is how I install Drush on CentOS systems that have H-Sphere installed as a control panel
1 - Grab a copy of Drush and untar it in your shared folder
sudo wget --quiet -O - http://ftp.drupal.org/files/projects/drush-7.x-5.9.tar.gz | sudo tar -zxf - -C /usr/local/share
(Note, change the link above you the link to the latest version of drush on Drupal.org.)
2 - Create a symbolic link to where Drush can be found on your server
sudo ln -s /usr/local/share/drush/drush /usr/local/bin/drush
3 - Get Drush to auto download the required "stuff"
Drush won't work yet as it won't know where to find php, so
4 - Open your bash_profile file and edit the PATH line from something like this:
to something like this (note the php path in this version):
5 - Reload your bash_profile
These notes are also available here.