you could use exec() and probably use the "top" or "ps" linux command and push that to output and parse through the output to see if it's running... maybe?? i've never done it and i'm not sure if it'll just show "apache", which i tend to think it will, i doubt it will show script.php (unless it's ran via shell).
you should think about using cron and only send a group of emails per cron run, once the email has been sent to, simply mark it as sent... so, send a group of 200 or so every 10 minutes or something like that using cron
hth,
stolzyboy