batch reverse dns lookup

[Andy Peters]

Hi i don't know if this is quite the group to ask this in (you are the dns
guru's ?) so feel free to offer alternative group suggestions

here's the problem, i have a list of domains (26,000+) in plain text format
(its a hosts file to be exact) and i would like to seperate the domains that
resolve to an ip from the ones that don't (to clean up the list and remove
invalid and dead entries)
any idea how i might achieve it ? i would of thought a quick bash or batch
script could do this but not having any experience in shell scripts i dont
know how i could do this
any help or pointers would be appreciated (i have access to
suse/knoppix/win*/)

cheers folks

Andy P