Ian,
I haven't had any experience on Windows so I can't answer that question. I do know it was written for Linux/Apache and that is how we use it. I am guessing you could make it work for Windows IIS with some work but why...
Now that we have invested sometime working with Joomla, we have been able to complete projects in no time! Joomla provides a great CMS and has turned out to be very Search Engine friendly
