I thought about learning php for the first time almost 18 months ago. I was looking for some thing small one click installation which will enable me to see php in action. I had IIS and tryed to get php to work with it. But because of some unknown reasons was not able to do it. Then I got xampp from
here.
It was just what I was looking for. It contains apache+php5+mysql5+perl in a simple installation. It got me started on php. After some time, I learned about wamp and tryed it. Since then, I am using wamp for my php development projects. wamp can also be configured to work with mod_asp.net and tomcat. Get wamp from here.
Although there isn't any special reason for using wamp instead of xampp, they both provide a simple to install single package for using php with apache on windows.