Add to Cart - Change Behaviour

[noisebug]

I have a small dropdown script that sorts added attributes in my Zen-Cart. Right now, when a customer selects a product I want them to be forced to select an attribute because products are priced by attributes.

"Selecting" price by attribute does not work the way I intend it to work, so I want to override the "Add to Cart" behaviour. I need it to check that the dropdown box I created has been selected.

Where could I modify this behaviour?

[Kim]

Have you tried just making the field required from the Attributes manager?

[noisebug]

Do you mean price manager, or attribute manager?

The problem I am having is this:

>Store here<

As you can see, since Zen dosn't chain attributes I wrote a script that hides certain attributes depending on what finish the user selects. But within those attributes is a "none" option. This is to ensure that if a user selects "print only", plaque mounting will remain as a "none" attribute and the cart will know not to charge them for extra.

The problem is, if the customer simply selects "printing" and "none", then Zen will still add the product to cart with 0 cost.

Maybe I can do it in another way, is it possible for Zen to make "none" as display only? I tried using the display only setting but it didn't work correctly.

Thanks for your help.

--edit--

On a side note, as you can see when you select the size dropdown it looks something like this:
60" x 42" (+$600)(+20lb)

Is it possible to take out the + and brackets and weight? So it will look like:
60" x 42" - $600