these are directions from 1and1
What do I need to consider if I want to use PHP 5?
With 1&1 Linux hosting packages you have the choice between PHP 4 and
PHP 5. To distinguish a script as PHP 5, simply name the script with the file
While the PHP developers have done their utmost to ensure compatibility, we cannot
guarantee that PHP 4 scripts will function 100% correctly under PHP 5.
Please note that in contrast to PHP 4, the default for the variable RegisterGlobals and allow_url_fopen is "off".
By default Apache uses PHP 4 for .php extension. If you don't want to rename all your
scripts to .php5 you can do the following:
Create a .htaccess file and place the following line AddType x-mapp-php5 .php in it.
This will tell Apache to use PHP 5 instead of PHP 4 for the extension .php in the
directory the .htaccess is placed and all sub-directories under it.