<?php $product = Mage::registry('current_product');?>
                    <?php $id = $product->getId();?>
                    <?php $name = $product->getName();?>
                    <?php $qty = $product->getStockItem()->getQty();?>
                    <?php if($qty==0):?>
                    <?php $user = Mage::getSingleton("customer/session"); ?>
                    <?php if(!($user->isLoggedIn())):?>
                    <?php echo "<form><input style="."text"." placeholder="."email".">"?>
                    <?php endif;?>
                    <?php echo "<p><a href="."sub/product/subthis/id/".$id."/name/".$name.">Send e-mail Action</a></p>";?>
                    <?php endif; ?>