Klemens, for example with the carousel featured products...
skin/smart_template/custom/featured_carousel.tpl
After...
Code:
<span class="price">{include file="currency.tpl" value=$f_products[product].price}</span>
Insert...
Code:
{include file="customer/main/alter_currency_value.tpl" alter_currency_value=$f_products[product].taxed_price tag_id="product_alt_price"}