I'm surprised nobody has presented a simple join-based solution yet...

#!/usr/bin/perl

use strict;
use warnings;

my $n_cols = 5;
my @data = ('1'..'12');

print "<table>\n";

while (@data) {
  print '<tr><td>'
      . (join "</td>\n    <td>", (@data, ('&nbsp;')x$n_cols)[0..$n_col
+s - 1])
      . '</td></tr>' 
      . "\n";
  @data = @data[$n_cols..$#data];
}

print "</table>\n";
[download]

Output:

<table>
<tr><td>1</td>
    <td>2</td>
    <td>3</td>
    <td>4</td>
    <td>5</td></tr>
<tr><td>6</td>
    <td>7</td>
    <td>8</td>
    <td>9</td>
    <td>10</td></tr>
<tr><td>11</td>
    <td>12</td>
    <td>&nbsp;</td>
    <td>&nbsp;</td>
    <td>&nbsp;</td></tr>
</table>
[download]