Here are the steps you need to take…

1. Download and Install Web Platform Installer (Web P.I.)
2. Install PHP (ISAPI Version) through Web P.I.
3. Install MySQL through Web P.I.
4. Download and Install ISAPI Rewrite Filter
5. Install WordPress through Web P.I.
6. Activate Multisite in WordPress
7. Download and Install phpMyAdmin (optional)

Step 1 – Download and Install Web Platform Installer (Web P.I.)

Web PI will save you a lot of trouble. Microsoft now supports open source web software for installation on a Windows IIS server. The Web PI automatically installs and configures your open source software so it works the first time with the least effort.

Click here to download the Web PI software installer. Download the installer and run it on your web server.

Step 2 – Install PHP through Web PI

WordPress code is written in PHP, and PHP is not native to an IIS server out of the box. The slightly complex job of installing PHP on the IIS server is automated by Web PI, simplifying the task. Open Web PI and click “Install” next to the latest release of PHP, be sure to install the ISAPI version (not CGI).

Step 3 – Install MySQL through Web PI

Open Web PI and install the latest release of MySQL. Easy.

Step 4 – Download and Install ISAPI Rewrite

The biggest challenge with getting IIS 6 to work with WordPress is that Windows does not have a native ISAPI rewrite filter in the web server. You have to download and install one. There are many choices, but Ionic’s ISAPI Rewrite Filter is free and it works, so why make it complicated, use this…

Click here to download Ionic’s ISAPI Rewrite Filter. Download the installer and run it on your web server.

Step 5 – Install WordPress through Web P.I.

Open Web PI and install the latest release of WordPress. Complete the WordPress installation through the browser. For WordPress Multisite it is best if your WordPress ionstallation is on the root directory of the website. When you have an active website and can log into the administration dashboard, you are done with this step. I’m assuming a basic WordPress installation is no problem for you. If you are having challenges, there are many resources online that can help you with WordPress installation challenges.

Step 6 – Activate Multisite in WordPress

WordPress Multisite gives you 3 choices of how to differentiate your multiple websites: subdomain, subdirectory, or domain mapping. For simplicity, I chose to go with the subdirectory option because it uses the ISAPI rewrite filter that we have already installed, and it requires no further installations.

NOTE: If you have to go with the subdirectory option, it involves wildcard directories, and you can click here to read about how to set up wildcard subdomains for WordPress. If you have to go with the domain mapping option, you can click here to read about how to set up domain mapping in WordPress.

So as I said, I went with subdirectory differentiation for ease of installation, and it seemed to be more compatible with IIS since it required fewer installations. In fact, we are done with all the required installations, and we will now only need to modify some code to finish up.

Add this line to your wp-config.php file and save the file:

define(‘WP_ALLOW_MULTISITE’, true);

On the left column in the dashboard, you will see a new link called “Network Setup” under “Tools.” Disable all of your plugins, and then click the “Network” link. Select “Sub-directories” for the Network type, give the network a title, and enter the admin e-mail address.

NOTE: If you see this error it’s because you installed WordPress more than 30 days ago: “Because your install is not new, the sites in your WordPress network must use sub-domains. The main site in a sub-directory install will need to use a modified permalink structure, potentially breaking existing links.” The work around solution is simply to ignore this message and change the line in the wp-config.php file that says “define( ‘SUBDOMAIN_INSTALL’, true );” to “define( ‘SUBDOMAIN_INSTALL’, false );” but be sure you backup your database before you try to go this route. If you are very worried about it, and you have a lot of posts, then you should consider using subdomains or domain mapping instead of subdirectories.

After you select the network type, title, and email, WordPress will display the code that is required for the wp-config.php and for the ISAPI rewrite filter. Copy the code that WordPress provides into the wp-config.php file as the WordPress directions explain. WordPress assumes the third chunk of code will be put into a file called “.htaccess” which would be correct if we were using Linux. Since we are using IIS 6 with the ISAPI filter we installed in step 4, we save the code that WordPress supplies for “.htaccess” but we save it in a file called “iirf.ini” and place that on the root of your WordPress web server.

That’s it.

To test your WordPress Multisite installation, log in again, and when you mouse over the top right link where it says “Welcome, [Your Name]” you should be able to see “Network Admin” Select “Network Admin” from that drop menu and you will access the network admin dashboard. Go to “Sites” on the left, set up a new site, and navigate to the new site through a browser. If you can do all that, then my work here is done, and you have a fully functioning WordPress Multisite installation working on your IIS 6 server.

Step 7 – Download and Install phpMyAdmin (Optional)

The phpMyAdmin software gives you an easy-to-use interface for managing your MySQL database. Some people prefer to use the native MySQL Command Prompt, but I prefer the nice GUI that phpMyAdmin gives me. All I had to do was download the code, unpack it, upload it to my server inside a directory called “pma,” and it just worked. If you have trouble, it’s probably just due to setting the right permissions for certain files, and the instructions that come with the code will tell you how to fix that, as well as other challenges. For me, I had no challenges at all. As I said, it just worked.

Click here to download the phpMyAdmin code in a ZIP archive. Download the zip archive, unpack it, and upload it to your server in a directory on your WordPress site (something like “yoursite.com/pma/”).

IMPORTANT: you will need to password protect the directory where you have the phpMyAdmin code because it can be used to create much havoc and should be locked down as much as possible.