I started wondering if I could run SquirrelMail on IIS. Turns out that it does work. With only minor tweaks, PHP installs just fine. I also installed MySQL. SquirrellMail requires ActivePerl if you want to use the config tools.
I have been hosting web sites in ASP for about 11 years now. I have a large investment in time and code in ASP. There are some tools that I want to work on in Java or PHP. I had those projects hosted on an old Blue & White G3 but the performance was never really there. It got to the point that the only thing running on the G3 was SquirrelMail.