If you are installing JOOMLA on the virtual private server means,

1.Log into the vps using ssh.

2.download the package

wget http://joomlacode.org/gf/download/frsrelease/11396/45610/Joomla_1.5.15-Stable-Full_Package.zip

extract the package

OR

If your are trying to install via cpanel means,

download and extract the package in the local machine

and upload it in the control panel >> file manager >> public_html

3.create a database in the  control panel

control panel >> mysql database wizard >> data base name >> create a database user >> add that user into the database >> give full privelage

4.open the browser http://yourdomainname

5.The browser will load the first page in our installation process

6.Give the database name,username,password and hostname of database

7.Once the settings are filled,click ok.

8.The next step is creating the admin account

9.once you filled the form click proceed.

10.Now the joomla is installed successfully.