Update Ok, This is better now. Here's how to use Win32::Lanman to do this.

use Win32::Lanman;
my $domain="DOMAINNAME";
my $pdc;
my $username;
my %info;

Win32::Lanman::NetGetDCName('',$my_domain,\$pdc);
Win32::Lanman::NetUserGetInfo($pdc, $username, \%info);
print "$_ == $info{$_}\n" foreach keys %info;
[download]

This is of couse assuming that you are after what you asked (ie full name of $env{username} ) vs the code you posted (ie enumerating all users in the domain)