dig/nslookup

Hello,

Not really related to bind, specifically. But maybe someone
could let me know where I could find the answer.

I have like 3000 IP that I would need to do reverse lookups
on them, I'll do the request using our nameservers, but is there
a sleep I should do between each lookups ?

And does anyone have a script that could help me to do all these lookups
in one shot and so that I have all the dnsname associated with the IP
in ascending order by using the IP, guess I'll have to do the script by my
self,
argh! :P

Thanks!