Well this means your apache is not configured to treat .php files as PHP code and execute them instead of delivering them. There are basicly two steps involved to make this work, if your distribution doesn't do it for you:
1st make sure the PHP module gets loaded:
LoadModule php4_module /usr/lib/apache/1.3/libphp4.so
2nd tell the Apache about .php files and their mime type:
AddType application/x-httpd-php .php .phtml .php3