How can I specify php running on a linux machine to use a remote smtp server for sending mail. /usr/local/lib/php.ini states that the option is only available for win32 environments. Any help is definitely appreciated.
No clue, because using the standard mail() is usually adviced against.
Try using an SMTP class (as found all over the place, even on this very site in the snippets section). That will let you specify everything, and it's faster too.