Others have already answered your specific question, but as a general reminder... When you don't know how to do it in Perl, but you do know how to do it at your DOS prompt (or equivalent), it's useful to know that backticks execute a system/shell command:
my $result = `ren $original_filename $new_filename`;
$result contains any output from the
ren command (which is silent if it succeeds), and
$? contains the numeric exit code from the command.
The command in the backticks isn't portable, of course, but since you're running into a Windows-specific problem that's unlikely to be a concern here.
$perlmonks{seattlejohn} = 'John Clyman';