Hmmm... no joy. I see that is *IS* getting the categories properly.... but it's not passing the selected category to the page with the buynow module. I tried changing the categories module to a different page (the categories all disappeared), then back again (the categories re-appeared)... but selecting a category DOES take it to the page with the buynow, it's just not filtering the categories at that point... it's just going to the buynow page with the "default" products listed, not the filtered ones.
Once I'm on the page with the buynow, I can select the category (another copy of the category module, set up the same way) and the filters apply...
Weird. It's like it's calling the page, but not passing the filter over to the buynow module.