TIMTOWTDI. :)
1. you can use gethostbyaddr

if($input =~ /^\d+.\d+.\d+.\d+$/) 
    {
        my $name = gethostbyaddr(inet_aton($input),AF_INET);
}
[download]

Other way, complicated, but gives u more accurate information is
2. Querying a website ARIN
Gives you much more information by typing the IP in the "Who is" page.