I'd pay money to have a free, "Express" version of IIS.
Putting the IIS installer on the Windows XP Pro CD is completely unworkable for the non-profits I work with. It might as well be stored on Mars.
Without IIS, I can't even consider ASP .NET, which means my only choice for web apps is PHP (or Ruby, I guess) on Apache.
I can install PHP, MySQL and Apache on Windows XP in a single click -- using the installer from http://www.apachefriends.org/en/xampp.html