Educating users about tags

I followed Neil’s (@neil) tutorial: “setting up a tag schema like Car Talk uses”.

I hoped to end up with something where a user could, up near the top of the page by the “Latest” and “Top” options, select first a Make and then a Model (well actually in my case select a state within the USA and then a city within that state). But I’m having trouble achieving that… the user just sees a single list of all the Makes/Models (states/cities).
When I look at the Car Talks forum site itself, there’s a prominent “Make & Model” button next to “Top”. But when one selects the button nothing at all seems to happen. I posted about that in their site feedback section and was informed that that’s been the case for weeks. I’m wondering if perhaps a recent forum software update has killed that capacity or at least made it dormant.
Is what I’m trying to do feasible? If so, I’d be grateful for any advice on how to accomplish it. Thanks!