I just posted a question on a similar issue, but I can tell you how I am producing a dynamic value list.
Create a separate table - I call my dynamic value list table - (Related to your first table) with the fields you want to appear in your second value list. Create a script that writes the selection from the first value list into a field on the dynamic table, into the appropriate field. Then create a value list from the values of the dynamic table / value field.
Hmmm, "Ferrous" and "Non-Ferrous" Metals--makes me wonder if you work in the Scrap Metals trade like I do currently... ;-)
Conditional value lists do not normally require a script to implement.
Here's a basic primer on conditional value lists found in the KnowledgeBase: http://help.filemaker.com/app/answers/detail/a_id/5833/kw/conditional%20value%20list
If that doesn't work for you, feel free to post back with more questions.