I ran your script and got this back.

$VAR1 = {
          'pop3_hosts' => [],
          'ftp_firewall' => undef,
          'ph_hosts' => [],
          'inet_domain' => undef,
          'time_hosts' => [],
          'daytime_hosts' => [],
          'smtp_hosts' => [],
          'test_exist' => 1,
          'test_hosts' => 1,
          'nntp_hosts' => [],
          'ftp_ext_passive' => 1,
          'snpp_hosts' => [],
          'ftp_testhost' => undef,
          'ftp_int_passive' => 0
        };
[download]

Most of those options, at least to me, seem non-critical for DNS resolution. As for the proxy variables, there no variables set and I am not using a proxy server either.

Okay, then... Can you try this?

$ strace -o 698729.out -econnect,sendto,recvfrom perl 698729.pl
[download]

The 698729.out file should start with something similar to this:

connect(3, {sa_family=AF_FILE, path="/var/run/nscd/socket"}, 110) = -1
+ ENOENT (No such file or directory)
connect(3, {sa_family=AF_FILE, path="/var/run/nscd/socket"}, 110) = -1
+ ENOENT (No such file or directory)
connect(3, {sa_family=AF_INET, sin_port=htons(53), sin_addr=inet_addr(
+"192.168.1.1")}, 28) = 0
sendto(3, "\321\263\1\0\0\1\0\0\0\0\0\0\2my\5yahoo\3com\0\0\1\0\1"...,
+ 30, MSG_NOSIGNAL, NULL, 0) = 30
recvfrom(3, "\321\263\201\200\0\1\0\2\0\0\0\0\2my\5yahoo\3com\0\0\1"..
+., 1024, 0, {sa_family=AF_INET, sin_port=htons(53), sin_addr=inet_add
+r("192.168.1.1")}, [16]) = 80
connect(3, {sa_family=AF_INET, sin_port=htons(80), sin_addr=inet_addr(
+"216.252.123.25")}, 16) = -1 EINPROGRESS (Operation now in progress)
connect(3, {sa_family=AF_INET, sin_port=htons(80), sin_addr=inet_addr(
+"216.252.123.25")}, 16) = 0
...
[download]

Note that 192.168.1.1 is my DNS nameserver and I don't have nscd running, so the fist ENOENT errors can be ignored. You can see that the DNS query got through since 216.252.123.25 is the IP address for my.yahoo.com and there's a connection to port 80 going on.

Hope that helps.

Update: renamed lwp-useragent.pl to OP's node ID, so it's clear where does the code come from.

Where did the lwp-useragent.pl script come from? I did not see it in the distribution.