I hope you're viewing that page at http://localhost/pagename.php and not file:///somepath/pagename.php. The former will be delivered by Apache (if it is running) and the latter will be opened directly by your Web browser.
Make certain that Apache is running. As root:
/etc/rc.d/init.d/httpd status
If it is not,
/etc/rc.d/init.d/httpd start
To make sure httpd is started when you reboot the system, open the Mandrake Control Center,open the System widget, and click on Services. Find the appropriate item and check it. This will create the appropriate symbolic links in your initscripts directories.
If Apache is running, but .php files are delivered up as source code, make sure /etc/httpd/conf/httpd.conf contains the appropriate instructions (below) and restart the server if necessary. You should have these two lines:
AddType application/x-httpd-php .php .php3
AddType application/x-httpd-php-source .phps