<?php
$product = Mage::getModel('catalog/product');
$product->setSku('sku');
$product->setAttributeSetId(1);
$product->setTypeId('simple');
$product->setName('Product name');
$product->setCategoryIds(array(1));
$product->setWebsiteIDs(array(1));
$product->setDescription('Description');
$product->setShortDescription('Short description');
$product->setPrice(0);
$product->setWeight(0);
$product->setVisibility(4);
$product->setStatus(1);
$product->setTaxClassId(0);
$product->setStockData(array(
'is_in_stock' => 1,
'qty' => 1
));
$product->save();
?>