You don't need the relationship, though you can use if if you wish, but you should not use either of your existing topic fields for this drop down as they store crictical information that should not be changed just to find records. Define another field and set it up with the needed value list and relationship for your searches. You may find that giving this new field global storage a good idea--especially if you have multiple people using your database at the same time.
Here's a thread on scripted finds that may give you some ideas on how to use a scripted find for this: Scripted Find Examples
Many thanks for the response. I'm still totally struggling, but I guess that's my lack of experience. i cant even get the relationships to work properly - back to the text books for me.
Feel free to use Post A Answer to post follow up questions where you describe what you've tried to set up and the results that you got when you tried that. There's a number of very generous people involved in this forum that can help steer you in the correct direction.