In Windows 2000 there is a management console that allows you to stop it, there should be something similar in XP. Also in the system tray you get an icon called PWS, this is another interface for IIS which allows you to stop it, the button is quite obvious.
Sorry if I seem a bit vague but I avoid IIS after finding the all powerful Apache!
If you are definate you won't use it you could always uninstall it completely (make sure you backup any websites that you have done and that you won't need ASP support as I don't think you can get ASP for Apache (god knows why you would want to anyway).
Anyway hope you get it up and running, PHP is easy and a great web-scripting language.