Fudnock: I just installed this today, following the instructions, and it does indeed show up in the WhereTo>Extras folder for me. If I were you I'd try the whole process again - sounds to me like the "unl" file isn't working properly to allow your Nuvi to "see" the Fodor's file. I used MapSource to find my Garmin Unit ID, entered it in the top of the Keygen, then changed the dropdown menu to "Custom Map" and entered "900" when prompted, then clicked the bottom "Generate" button to get the string. I opened the ".unl" file with Notepad, pasted the string into the file, and then clicked "File>Save." I copied both the new D***.unl file and the D***.gpi file to the "Garmin>Poi" folder and when I restarted the Nuvi (I have the 500) it showed up. I'd recommend trying the whole process again and see if it makes a difference!
Good luck - and also - you're lucky that Denver is one of the areas covered by the application. I live in the Rochester, NY area and I think the closest area covered by this application is NYC, hundreds of miles away. Maybe Niagara Falls is... dunno. Best of luck!