I'm never played with Curses before, but it's been on my todo list for years...

$w=newwin(1,1,40,40);

You've got your arguments to newwin incorrect.

$ man newwin
...
WINDOW *newwin(int nlines, int ncols, int begin_y, int begin_x);
[download]

use Curses;

initscr;
my $w = newwin(40,40,1,1);
$w->addstr(20,20,"Hello");
$w->refresh;
endwin;
<>;
[download]

Works for me.

Update: Fixed borked link