The sample code posted by beech above shows how to use "pack" to get four panes arranged in the 2x2 pattern you want.

But personally, for this sort of thing, I'd use the "grid" geometry manager:

#!/usr/bin/perl
use strict;
use warnings;
use Tk qw/tkinit/;

my $mw = Tk::MainWindow->new;
my $topleft  = $mw->Pane(qw'-bg pink'   )->grid(qw/ -column 0 -row 0 /
+);
my $topright = $mw->Pane(qw'-bg purple' )->grid(qw/ -column 1 -row 0 /
+);
my $botleft  = $mw->Pane(qw'-bg green'  )->grid(qw/ -column 0 -row 1 /
+);
my $botright = $mw->Pane(qw'-bg orange' )->grid(qw/ -column 1 -row 1 /
+);
$mw->MainLoop;
[download]

So, what did you actually try that was different from either of these two examples?