I installed XAMPP Version 1.4.13 on Windows XP. The first thing that impressed me about XAMPP was that the installation didn't require a reboot. Every other lazy program seems to need a reboot after installation, but this one doesn't. And it's server software!
XAMPP is started in a console window. This way it's not running when you don't need it. When you first view localhost in the browser, there is an interface to let you test your installation and view demo applications. There are also links to phpMyAdmin, so it's easy to go in and start setting up your database. I'm also impressed at the performance. My laptop didn't seem to mind running the server.
If you're doing PHP and MySQL development, try this out. It's only 25 megs, it takes no time to get up and running, and its easy to uninstall -- just delete the folder. You have nothing to lose.