IIRC, PWS was so embarassing from a security point of view that Microsoft didn't even recommend it as of 98SE.
But, then I'm a Apache/'Nix geek.
IIS has gotten lots of bad attention as well. Apache, however, will also have an issue with security now and then.
How big an intranet? Put a Pentium II & mobo in a toaster case with a HDD, add NetBSD and a HDD, Apache/mod_php, and remain vigilant. You'll never have to upgrade hardware, unless the toaster has a lot of crumbs still in it....