Always a million ways to skin a cat (esp. in this case), and here is another...

#initialize array
@array = (12,7,4);

$i=0;
foreach (@array) {
   #Throw in a hash to look up in a second
   $hash{$_} = $i;
   $i++;
}

#sort it, loop through, and look up from hash from above
foreach (@num_sorted_array = sort { $a <=> $b } @array) {
  print "$_ came from \$array\[$hash{$_}\]\n";
}
[download]

Probably not the most efficient way, but simple enough.

Regards,
nandeya