Well, this is a bit of a drag, I suppose -- and certainly it's something that the DialogBox doc should be more clear about -- but just using "add(Widget)" isn't enough... you have to "->pack()" it, too. Here's a nutshell example of a version that seemed to work for me; it's not pretty, but...

my $addGoalButn = $features->Button(-text=>'Add Goal',
                                    -command=> \&mkDialogBox,
                                    )->pack();

sub mkDialogBox {
    $n_prompt = $main->DialogBox(-title=>"Add a \$ value and explanati
+on",
                                 -buttons=>["OK","Cancel"]);
    $n_prompt->add(Label, -text=>"\$")->pack(-side => 'left');
    $numNewGoal = $n_prompt->add(Entry)->pack(-side => 'left');
    $descNewGoal = $n_prompt->add(Text, -height=>'5',
                                  -width=>'30')->pack(-side => 'left')
+;
    $n_prompt->Show();
    $num = $numNewGoal->get();
    $desc = $descNewGoal->get("1.0", "end");
#paid upgrade option: rewrite below for Excel/SQL connectivity
    $desc =~ s/\s*$/\n/;
    (open(GF, ">>$file_goals") and
    print GF join("\n", $num, $desc) and
    close GF) or warn "unable to save date to $file_goals\n";
}
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Note, BTW, a couple subtle changes in the "upgrade" part at the end. (1) it looks like your intent was simply to append to the end of a file, but if it doesn't exist yet, opening "+<$file" will fail. Using ">>$file" will always work (unless there's a disk or permission problem). (2) You don't want to use '\n', unless you really want the literal 2-character string '\n' to show up in the output (i.e. to look exactly like '45\nComment'). (3) It's worth your while to normalize the final whitespace on whatever the user typed into the "description" field; other formatting may be worthwhile as well.