Here's a way that makes gratuitous use of map! ;)

use strict;

while (<DATA>) {
    chomp;
    my $val = join '/', map {$_ + 0} (split /\//, $_);
    print "$val\n";
}

__DATA__
12/09/2004
01/15/2003
03/09/2004
10/28/2002
004/00003/02003
[download]

Isn't Perl wonderful?