$ perl www_whacker.pl --start 200000 --limit 100000 >out1 &
$ perl www_whacker.pl --start 300000 --limit 100000 >out2 &
$ perl www_whacker.pl --start 400000 --limit 100000 >out3 &
$ # wait for all jobs to complete, then you can join all
$ # the results together:
$ cat out1 out2 out3 >output