Ping!

Hi All: I'm trying to make a script that will check if several computers are online by pinging them (or any other suggested method, I know no others). I tried using fsockopen but, what port do I try? Most computers I want to locate are Win95/98, including the server running apache 1.3.12 and php 4.0.2, and all they have is UDP 139 protected with a fix that hides it. If I try to open a connection on an arbitrary port number, I always get an error since the target computer won't answer on that (or any other) port, so even if the computer is online, I get an error just as if it isn't online. I can use MS-DOS' "ping" command, and then check the output, but I'd like to keep my script as platform-independent as possible. Any ideas? Thanks, Gonzalo Vera.