Howdy AM,
  crypt() in Perl encrypts a string exactly like crypt(3) in your C library. Consulting your crypt(3) manpage will probably show you that if crypt() is provided a salt that begins with the three characters '$1$' followed by at most 8 characters, it will use an MD5-based algorigth.

Changing your code to:

my @chars = ('a'..'z', 'A'..'Z', 0..9);
my $password = do {{
  local $_ = join "" => map {$chars [rand @chars]} 1..8;
  redo unless /[a-z]/ && /[A-Z]/ && /\d/;
  $_;
}};
my $salt = '$1$' . join '',
   ('.', '/', 0..9,
   'A'..'Z', 'a'..'z')[ map { int rand 64 } 0 .. 7 ];
my $encrypted_pass = crypt($password, $salt);
[download]

should result in an MD5 passwd (depending on your systems crypt(3), of course).

Hope that helps,

-- dug