The templates involved are product_details.tpl and products_list.tpl, but their location depends upon which template set you're using.
They are located in the customer/main folder of the template set, OR, one is located there and the other is located in the skin/common_files/customer/main folder. Clear as mud?
Warning! There's a product_details.tpl located in the
skin/common_files/main folder and it is for the Admin side. You don't wanna mess with that one.
If'n you is looking for some detailed info on how to hack that code you found to work with the templates, I'm back to being an
anyone and can't help ya. Sorry.