In a new post to his MSDN blog Brian Swan looks at how you can run WordPress on SQL Server:

In any case, the cat is out of the bag with this new blog: WordPress on Microsoft. Now, you might ask why the BLEEP is Microsoft doing this? But that is answered here: Why the BLEEP is Microsoft doing this? You might also ask how is Microsoft doing this? The answer to that question is here: WordPress on SQL Server: Architecture and Design. Finally, you might ask how do I do this? Again, the answer is here: Installing WordPress on SQL Server. (These guys seem to have all their bases covered.)

His previous install guide assumes that you're starting from scratch and you're using the Web Platform Installer to get everything installed and working. This guide, however assumes that you already have the web server (IIS), PHP and SQL Server all set up and ready to go.