How do I configure Apache to Run Background PHP Processes on Win 2003 w/Apache 2.2?

Question

I have a script, testforeground.php, that kicks off a background script, testbackground.php, then returns while the background script continues to run until it's finished.

Both the foreground and background scripts write to the output file correctly when I run the foreground script from the command line using php-cgi:

C:\>php-cgi testforeground.php

The above command starts a php-cgi.exe process, then a php-win.exe process, then closes the php-cgi.exe almost immediately, while the php-win.exe continues until it's finished.

The same script runs correctly but does not have permission to write to the output file when I run it from the command line using plain php:

C:\>php testforeground.php

AND when I run the same script from the browser, instead of php-cgi.exe, a single cmd.exe process opens and closes almost instantly, only the foreground script writes to the output file, and it doesn't appear that the 2nd process starts:

http://XXX/testforeground.php

Here is the server info:

OS: Win 2003 32-bit
HTTP: Apache 2.2.11 
PHP: 5.2.13
Loaded Modules:  core mod_win32 mpm_winnt http_core mod_so mod_actions mod_alias mod_asis mod_auth_basic mod_authn_default mod_authn_file mod_authz_default mod_authz_groupfile mod_authz_host mod_authz_user mod_autoindex mod_cgi mod_dir mod_env mod_include mod_isapi mod_log_config mod_mime mod_negotiation mod_setenvif mod_userdir mod_php5

Here's the foreground script:

<?php

ini_set("display_errors",1);
error_reporting(E_ALL);

echo "<pre>loading page</pre>";

function run_background_process()
{
 file_put_contents("0testprocesses.txt","foreground start time = " . time() . "\n");
 echo "<pre>  foreground start time = " . time() . "</pre>";

 $command = "start /B \"{$_SERVER['CMS_PHP_HOMEPATH']}\php-cgi.exe\" {$_SERVER['CMS_HOMEPATH']}/testbackground.php";

 $rp = popen($command, 'r');
 if(isset($rp))
 {
  pclose($rp);
 }

 echo "<pre>  foreground end time = " . time() . "</pre>";
 file_put_contents("0testprocesses.txt","foreground end time = " . time() . "\n", FILE_APPEND);
 return true;
}

echo "<pre>calling run_background_process</pre>";

$output = run_background_process();

echo "<pre>output = $output</pre>";

echo "<pre>end of page</pre>";
?>

And the background script:

<?php
$start = "background start time = " . time() . "\n";
file_put_contents("0testprocesses.txt",$start, FILE_APPEND);

sleep(10);

$end = "background end time = " . time() . "\n";
file_put_contents("0testprocesses.txt", $end, FILE_APPEND);
?>

I've confirmed that the above scripts work correctly using Apache 2.2.3 on Linux.

I'm sure I just need to change some Apache and/or PHP config settings, but I'm not sure which ones. I've been muddling over this for too long already, so any help would be appreciated.