I've got a script that downloads files queued from a server, and it's
launched by a Windows Scheduled Task that launches every minute. My
understanding of the default behavior is that if the task is still
running a minute later when it's time to launch again, a duplicate
thread will not be launched.

The remote server administrator wants me to launch multiple threads
all day - in my mind the wrong choice, since multiple download threads
slow everyone one, but that's what he wants.

Anyone know if there's a way to make Windows Scheduled Task launch a
new thread of the PHP script, regardless of whether it's already
running?

Your assumption is semi-correct, mostly because of your choice of language. If you would have asked about launvhing another download process, then you would be wrong.

A new _process_ *is* spawned by the Windows Scheduled Task launcher.

Here's a proof.

test.bat

start c:\php\php.exe test.php
start c:\php\php.exe test.php

test.php:

<?php
sleep(20)
print "slept 20 seconds";
?>


Double click on test.bat, you should see 'slept 20 seconds' printed
twice.