The fields I want to use for dynamic filters aren't showing as available. How do I change that?

The Help text here  http://www.quickbase.com/user-assistance/Default.html#dynamic_filters.html  near the bottom explains which field types are available as Dynamic filters. In general,  formula fields for example, are not eligible.  You also need to ensure that the field(s) you want are set to be searchable in their field properties.