Wow! Thanks for the speedy response!
Okay, this is it: I created a page with "hello.php" filename using notepad. I'm using Windows XP SP2, btw. I saved it to C:\xampp\htdocs\new folder. But when I tried accessing it; typing http://localhost/hello.php
or C:\xampp\htdocs\new\hello.php, the browser (Firefox 3) suddenly asks me to save the file. Why is it happening?