That said, you get what you want if you pack the Label and Entry widgets into a frame of their own and anchor that at the bottom of $left_frame before adding the other widgets (see also the -after and -before arguments to pack() for an alternative):

#!/usr/bin/perl

use Tk;
my $mw = MainWindow->new();

$left_frame   = $mw->Frame->pack(qw(-fill both -expand 1));
$bottom_frame = $left_frame->Frame->pack(qw(-side bottom -expand 1 -fi
+ll x));

$left_frame->Label(-text => "Perl Chat Client v$VERSION")
              ->pack(-side => 'top',
                     -anchor => 'nw',
);
$status = $left_frame->Text (-width => 40,
                                -height => 30,
                                -wrap => 'word')->pack(qw(-expand 1 -f
+ill both));

$status->tagConfigure(section,
      -font => '-adobe-helvetica-bold-r-normal--14-140-75-75-p-82-iso8
+859-1');

$status->bind('<Double-1>', \&pick_word);
$bottom_frame->Label(-text => 'Global Message:')->pack(qw(-side left -
+anchor s));
$gm_quick = $bottom_frame->Entry (-width => 26)->pack(qw(-side left -a
+nchor s -fill x -expand 1));
$gm_quick->bind('<KeyPress-Return>', sub { 
                                           send_msg_all($gm_quick->get
+());
                                           $gm_quick->delete(0,'end');
                                     }
);
MainLoop;
[download]

The qw(-fill x -expand 1) arguments to pack() are provided for the text and entry widgets to resize nicely.

_($_=" "x(1<<5)."?\n".q·/)Oo.  G°\        /
                              /\_¯/(q    /
----------------------------  \__(m.====·.(_("always off the crowd"))."·
");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}