Change Magento default status for duplicated products

Try this:

Create: app/code/local/MagePal/EnableDuplicateProductStatus/etc/config.xml

<?xml version="1.0"?>
<config>
    <modules>
        <MagePal_EnableDuplicateProductStatus>
            <version>1.0.1</version>
        </MagePal_EnableDuplicateProductStatus>
    </modules>

    <global>
        <models>
            <enableduplicateproductstatus>
                <class>MagePal_EnableDuplicateProductStatus_Model</class>
            </enableduplicateproductstatus>
        </models>
         <events>
            <catalog_model_product_duplicate>
                <observers>
                    <enableduplicateproductstatus>
                        <type>singleton</type>
                        <class>enableduplicateproductstatus/observer</class>
                        <method>productDuplicate</method>
                    </enableduplicateproductstatus>
                </observers>
            </catalog_model_product_duplicate>
        </events>
    </global>
</config>

Create: app/code/local/MagePal/EnableDuplicateProductStatus/Model/Observer.php

class MagePal_EnableDuplicateProductStatus_Model_Observer 
{
    /**
     * Prepare product for duplicate action.
     *
     * @param Varien_Event_Observer $observer
     * @return object
     */
    public function productDuplicate(Varien_Event_Observer  $observer)
    {
        $newProduct = $observer->getEvent()->getNewProduct();
        $newProduct->setStatus(Mage_Catalog_Model_Product_Status::STATUS_ENABLED);

        return $this;
    }
}

Create: app/etc/modules/MagePal_EnableDuplicateProductStatus.xml

  <?xml version="1.0"?>
    <config>
           <modules>
                  <MagePal_EnableDuplicateProductStatus>
                          <active>true</active>
                          <codePool>local</codePool>
                  </MagePal_EnableDuplicateProductStatus>
           </modules>
    </config>

Then clear cache and try duplicating a product.

read more @ :

http://magento4u.wordpress.com/2009/06/08/create-new-module-helloworld-in-magento/

http://www.magentocommerce.com/wiki/5_-_modules_and_development/0_-_module_development_in_magento/customizing_magento_using_event-observer_method

make a new product active by default in magento