Is there any way to create a query (or macro?) that creates a value list based on a value from another list?

For example, say I had a field called "Topics" and I chose "health" from the list - is there a way to make it such that the "Subtopics" field would automatically bring up subtopics (HIV, nutrition, etc) related to health? Rather than list all subtopics of every main Topic?

Yes, you are talking about cascading combo boxes, where a selection in one combo box is used as criteria in another combo box.

Search this site for cascading combo boxes. Or see Candace Tripp's web site for an example.