<?php // Previous and Next product links in product page

$_product = $this->getProduct();

if(!$_product->getCategoryIds())
return; // Don’t show Previous and Next if product is not in any category

$cat_ids = $_product->getCategoryIds(); // get all categories where the product is located
$cat = Mage::getModel(‘catalog/category’)->load( $cat_ids[0] ); // load first category, you should enhance this, it works for me

$order = Mage::getStoreConfig(‘catalog/frontend/default_sort_by’);
$direction = ‘asc’; // asc or desc

$category_products = $cat->getProductCollection()->addAttributeToSort($order, $direction);
$category_products->addAttributeToFilter(‘status’,1); // 1 or 2
$category_products->addAttributeToFilter(‘visibility’,4); // 1.2.3.4

$cat_prod_ids = $category_products->getAllIds(); // get all products from the category
$_product_id = $_product->getId();

$_pos = array_search($_product_id, $cat_prod_ids); // get position of current product
$_next_pos = $_pos+1;
$_prev_pos = $_pos-1;

// get the next product url
if( isset($cat_prod_ids[$_next_pos]) ) {
$_next_prod = Mage::getModel(‘catalog/product’)->load( $cat_prod_ids[$_next_pos] );
} else {
$_next_prod = Mage::getModel(‘catalog/product’)->load( reset($cat_prod_ids) );
}
// get the previous product url
if( isset($cat_prod_ids[$_prev_pos]) ) {
$_prev_prod = Mage::getModel(‘catalog/product’)->load( $cat_prod_ids[$_prev_pos] );
} else {
$_prev_prod = Mage::getModel(‘catalog/product’)->load( end($cat_prod_ids) );
}
?>