php script visible in Dreamweaver but not in browser, any ideas?

creating my first php site and I'm just making sure I have everything setup. I typed a very simple script:

<?php echo "Hello World"; ?>

it displays just fine in开发者_JAVA技巧 Dreamweaver's design view but when I open it in Firefox it doesn't display. Any ideas why?

Using xampp, have apache running.

What displays when you try to view the file on in FireFox? (blank page? error? etc?) And ensure you are viewing the file by localhost/file_name/... NOT c:\..