Conditional Value list question

I have two interrelated tables. One contains an insertion ID (auto serial number), and Media Name (user entry text). The other contains a creative order number (auto serial number), Media Name (value list from first table), and Insertion ID (value list from first table). The insertion ID on Table 2 is based on the Media Name relationship, so that the drop-down list will only display insertion IDs created for that specific media, instead of all existing insertion IDs. Back on Table 1, I want to create the same type of conditional value list for the creative order number. I am able to narrow it down to just displaying the creative order IDs with that same Media name, but I would like to instead display the creative order #'s attached to that Insertion number. Any help would be greatly appreciated.