(You'll probably have to click in the window to give it focus. And you'll probably have to leave your mouse in the frame, too. If you know how to give buttons focus programatically, feel free to share, won't you?)

<?
  /* sprite has one letter per frame */

  $p = new SWFSprite();
  $p->add(new SWFAction("stop();"));

  $chars = "abcdefghijklmnopqrstuvwxyz".
	   "ABCDEFGHIJKLMNOPQRSTUVWXYZ".
           "1234567890!@#$%^&*()_+-=/[]{}|;:,.<>?`~";

  $f = new SWFFont("_sans");

  for($n=0; $nremove($i);
    $t = new SWFTextField();
    $t->setFont($f);
    $t->setHeight(240);
    $t->setBounds(600,240);
    $t->align(SWFTEXTFIELD_ALIGN_CENTER);
    $t->addString($c);
    $i = $p->add($t);
    $p->labelFrame($c);
    $p->nextFrame();
  }


  /* hit region for button - the entire frame */

  $s = new SWFShape();
  $s->setFillStyle0($s->addSolidFill(0, 0, 0, 0));
  $s->drawLine(600, 0);
  $s->drawLine(0, 400);
  $s->drawLine(-600, 0);
  $s->drawLine(0, -400);


  /* button checks for pressed key, sends sprite to the right frame */

  $b = new SWFButton();
  $b->addShape($s, SWFBUTTON_HIT);

  for($n=0; $naddAction(new SWFAction("

setTarget('/char');
gotoFrame('$c');

    "), SWFBUTTON_KEYPRESS($c));
  }

  $m = new SWFMovie();
  $m->setDimension(600,400);
  $i = $m->add($p);
  $i->setName('char');
  $i->moveTo(0,80);

  $m->add($b);

  header('Content-type: application/x-shockwave-flash');
  $m->output();
?>