I understand Xitami can run php, and I used it back in my NT days. It's very fast and efficient, and very easy to setup and administer.
OmniHTTPD is almost as fast, and even easier to install, and I remember seeing it used with php somewhere.
If you're gonna do serious database work, THEN look at a linux box for the database, or as a minimum NT. 95/98/ME are just not stable enough for a heavily worked database.