To proceed with the installation of Wordpress on SQL Server and IIS, first of all, you need to do the following steps

1. Create a database on SQL Server that will be used by Wordpress
2. Create login that can access to the just created database and put the user into ddladmin, db_datareader, db_datawriter roles
3. Download and unpack Wordpress 3.3.2 (latest version as of 27 May 2012) zip file into a directory of your choice
4. Download the wp-db-abstraction 1.1.4 (latest version as of 27 May 2012) plugin from wordpress.org website

Now that the basic action has been done, you can start to setup and configure your Wordpress installation.

Unpack and follow the instructions in the README.TXT file to install the Database Abstraction Layer. Mainly you have to:

• Upload wp-db-abstraction.php and the wp-db-abstraction directory to wp-content/mu-plugins.  This should be parallel to your regular plugins directory.  If the mu-plugins directory does not exist, you must create it.
• Put the db.php file from inside the wp-db-abstraction.php directory to wp-content/db.php

Now you can create an application pool in IIS like the following one

Create a website, using the above Application Pool, that points to the folder where you unpacked Wordpress files.

Be sure to give the “Write” permission to the IIS account, as pointed out in this (old, but still quite valid) installation manual:

http://wordpress.visitmix.com/development/installing-wordpress-on-sql-server#iis

Now you’re ready to go. Point your browser to the configured website and the Wordpress installation screen will be there for you.

When you’re requested to enter information to connect to MySQL database, simply skip that page, leaving the default values. If you have installed the Database Abstraction Layer, another database installation screen will appear after the one used by MySQL, and here you can enter the configuration information needed to connect to SQL Server.

After having finished the installation steps, you should be able to access and navigate your wordpress site.  A final touch, and it’s done: just add the needed rewrite rules

http://wordpress.visitmix.com/development/installing-wordpress-on-sql-server#urlrewrite

and that’s it!

Well. Not really. Unfortunately the current (as of 27 May 2012) version of the Database Abstraction Layer (1.1.4) has some bugs. Luckily they can be quickly fixed:

Backslash Fix
http://wordpress.org/support/topic/plugin-wp-db-abstraction-fix-problems-with-backslash-usage

Select Top 0 Fix
Make the change to the file “.\wp-content\mu-plugins\wp-db-abstraction\translations\sqlsrv\translations.php” suggested by “debettap”   http://sourceforge.net/tracker/?func=detail&aid=3485384&group_id=315685&atid=1328061

And now you have a 100% working Wordpress installation on SQL Server!

Since I also wanted to take advantage of SQL Server Full Text Search, I’ve created a very simple wordpress plugin to setup full-text search and to use it as website search engine:

http://wpfts.codeplex.com/

Enjoy!