How to run php programs on local computer?

[joe at actionline.com]

Brian last wrote (in part): [example html code snipped]
> If you paste the above code into a file named /var/www/index.php you
> will see the result.  Just point your web browser at
> http://127.0.0.1/index.php

I followed this to the letter, but when I enter
http://127.0.0.1/index.php in the browser address field,
I got a pop-up asking this:
"What should Firefox do with this file?"
(*) Open with (KWrite (default) is the only option shown)
( ) Save File

Also tried changing owner and group from root to joe.
Still did not work.

Also tried using my own IP address: http://192.168.0.87/index.php
Still did not work.

Also tried:  file:///var/www/index.php
Still did not work.

Also tried: http://127.0.0.1/var/www/index.php
Still did not work.

Also tried: http://192.168.0.87/var/www/index.php
Still did not work.

Can't seem to find the magic formula.