I've tidied the code up a bit and made the change that you requested. The simplest way to do what you wanted with the table rows is to use map as I've demonstrated below.

#!/usr/bin/perl -w
use strict;
use CGI qw/ :standard  /;

my %hash;
my $key;
my %names;
my $value;
my $i;

foreach $i (1..10) {
  $key = $i % 3;
  $value = $i;
# The next line is not required due to autovivification
#  $hash{$key} ||= [];
  push @{$hash{$key}}, $value;
}

my @names;
foreach $key (0..2) {
  $names[$key] = "key $key";
  print p(join( '/', @{$hash{$key}}), " modulo 3 give $key\n");
}

print start_form();

print table(Tr([th(@names),
                map { td(popup_menu(-name=>'0',
                                    -values=>[@{$hash{$_}}],
                                    -default=>$hash{$_})) } keys %hash
+]));

print end_form();
print end_html();
[download]

--
<http://www.dave.org.uk>

"Perl makes the fun jobs fun
and the boring jobs bearable" - me