Anyone?   Bueller?   {grin}

Update:
Thanks to good monk tye for a polite RTFM   8^)   perldoc Term::ReadKey indicates that it just *might* support timeout internally.   I'm still experimenting with the syntax - will post results.

Update:
No go.   "Non-blocking ReadLine is not supported on this architecture" with ActivePerl 5.6 on Win2k, but runs fine on Debian 2.2r3

$!/usr/bin/perl -w

use strict;
use Term::ReadKey;
use Term::ReadLine;

ReadMode('noecho');
print 'enter password:';
my $pass = ReadLine(5);
ReadMode('restore');
unless (defined($pass)) {
    print "\n\nSorry, you waited too long.\n\n";
    exit;
    }
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    muttering to himself...
    Don
    striving toward Perl Adept
    (it's pronounced "why-bick")