Mad_Griffith:
Ok, I've applied a model for each product.
http://keyitalia.eu/index.php?main_page=index&cPath=1_7_66
Now, I've realized that there is chance the "model" field is not appropriate for my goal, which is the following: I'm building a shop selling pictures, where each category is named after the general size (for example, "large size", "small size", "medium size") of the pictures which will be filed in. Inside each category, I would like to put a drop-down menu with the exact sizes (like "80x120 cm", "80x145", "90x120", and so on). After choosing one of those "exact sizes", a list of the pictures of that size should be generated.
Is my goal clear? I think that the model-thing is not really useful for me... thus I should think about something else (though I don't know what I can use, since I'm new to Zen Cart)...
You could use "manufacturer" for that, if you won't be using it. Under "Catalog", go to "manufaturers", and create all the sizes you need as a "manufacturer". Then for each product, when you're adding it, choose the "manufacturer" from the drop down menu. Then the customer will be able to choose the size, and only see those sizes displayed. You can change the text seen next to the drop down menu to "Choose Size:" in (I think) includes/languages/YOUR_LANGUAGE/index.php:
define('TEXT_SHOW', 'Filter Results by:');