Running the vBulletin Install Script 
Once all the vBulletin files have been successfully uploaded to your web server, you will need to run the vBulletin Installation Script in order to prepare your database.

The Installer runs as a PHP script using your web browser. To start the installation process, open your browser and type the HTTP address of your forums directory, followed by /install/install.php, then hit the <Enter> key or press the [Go] button to open the script.

The first thing you will see from the install script is a log in prompt, asking you to enter your customer number. This is done to prevent other users from accidentally stumbling across your install script and running it. Only you should know your customer number.
Your customer number is the string of numbers and letters used as the login user name for the vBulletin Members' Area. You should type your customer number carefully to avoid errors. Note that your customer number is not the same as your vBulletin license number.

When you have entered your customer number, hit the [Enter Installer] button and you should be taken to the first step of the install script. If after hitting the [Enter Installer] button you are brought back to the customer number entry dialog, there was an error verifying your customer number. Please check for mistakes and try again.

The first page of the installer script will greet you and give you some basic instructions relating to what will happen during the rest of the install process.

Having read the information on the welcome page of the installer, you can click the large [Next Step] button at the bottom right of the window to proceed to the next step of the installer.
Certain browser plug-ins, most notably the popular Google Toolbar can have an adverse effect up the vBulletin installation and upgrade scripts. We recommend that all browser plugins be disabled while running install and upgrade scripts for vBulletin.
Clicking the [Next Step] button will take you to the first installation step, which tests that your config.php file exists and is readable by the system.

A further click will bring you to step 2, in which the installer attempts to connect to the database. If the connection is made successfully, the installer will ask you if you want to empty the database. If you click this link your database will be totally emptied. All data stored in that database (including any data not related to vBulletin) will be irreversibly erased.
Don't click the 'empty database' link unless you are really sure that's what you want to do!
The next few steps offer no choices during the installation process, other than to click the [Next Step] button at the bottom of the page to proceed to the next step.

However, you will soon be present with a page entitled Obtain Some Default Settings. This page does not have a [Next Step] button, as it requires that you fill in a few details about how you are installing vBulletin.

The settings required here are:
BB TitleThis is the title you will give to your vBulletin forums. It appears in the title of every page, and items such as notification emails sent from vBulletin to your members will identify the sender using this name. (BB Title is short for bulletin board title).
Homepage TitleLess important than the BB Title, this setting is used for a link at the bottom of every page which points to the address specified in Home URL (see below). It represents the title of your web site.
BB URLThe BB URL setting is very important. It represents the URL that people should visit in order to find your vBulletin forums. The system will make a best-guess at filling-in this setting automatically, so you should only change it if the given value is definitely wrong. Note that this setting should not end with a slash (/) character.
Home URLThis is the web address of your main web site, and is used in conjunction with the Home Title setting to create a link to your web site from the bottom of each forum page.
Cookie PathWhen cookies are stored on visitors' computers, this setting will be used to define to what location on your server the cookies apply. Unless you have a reason to change this setting it's probably a good idea to leave it at the default value of '/' (meaning that the cookies can be read by the entire site).
Cookie DomainRather like the cookie path setting, this allows you to specify the domain to which cookies belong. Generally speaking this setting can be left empty.
After filling in these values and clicking through the next few screens you will be asked to set yourself up as the forum administrator.

You will need to provide a username with which you are going to log-in, together with a password and an email address. These will be the details with which you will log in to your installed vBulletin board.
When choosing a password, we would suggest a combination of letters, numbers and punctuation characters in both upper and lower case, and a length of at least eight characters.
Fill in the required boxes and hit the [Continue] button to proceed with the installation process.

After a few pages the installation process will complete, and you will be presented with a link to your Admin Control Panel. Before clicking this link, you should open up your FTP client application again and browse to the install folder inside your forums directory.

You should delete the install directory, and all of its files now as a security precaution. Once you have deleted these files/folders you can return to the installer script and click the link to enter the Administrator Control Panel of your freshly installed vBulletin!
You will not be able to enter the Admin Control Panel until you have deleted the install directory.
Trevor Matthews 28th Oct 2010, 01:25pm
If installing on a 1and1 server running the installer produces an error.
Create a WordPad file called .htaccess with this text in it AddType x-mapp-php5 .php
Save and upload to the forum root folder. Run the installer again.