If you are unfamiliar with the term; PHP is a very popular open source web development language.
Usage wise, it is arguable by many which language is “superior”, but they both have their pros and cons. After using both extensively, I would have to say I am more preferable to .Net, but PHP still has it’s uses.
One major disadvantage though in my opinion, is having to require separate servers or services to utilize both. Although Apache web server is very popular, and the usual choice for delivering PHP content, it is much easier to configure IIS for a windows or .Net developer or admin, and streamlines the process a little more.
I was a little skeptical of using PHP on IIS6, however, I can trustfully say IIS7 is a good alternative to apache for your PHP applications, and would recommend it to anyone migrating from a windows environment or with developer staff that is cross-platform.
See references below for link to install and configure including a nice PHP Manager which plugs right in to your IIS management interface.