From POI Loader...
I've been messing around with the the TourGuide format for awhile now, but documentation is pretty slim. Here's what the POI Loader Help File says:
TourGuide is a feature available on compatible Garmin devices. TourGuide files include Custom POIs with descriptive .mp3 audio files. When you approach a TourGuide point, the .mp3 file plays and provides you with information about that point, much like a guided tour. TourGuide files must be saved as .gpx files.
NOTE: TourGuide files are usually created by third party developers.
To create TourGuide points, follow the steps for creating Custom POIs in MapSource and use the File/URL field to attach the appropriate .mp3 files to the points. The .mp3s must contain the word "TourGuide" in the file name to activate the TourGuide feature.
After you have created all your TourGuide points, save them as a .gpx file. See Creating Custom POIs in MapSource for more information.
After you have saved your TourGuide points in a .gpx file, you can save them on an SD card or load them on your compatible GPS unit using Express Mode or Manual Mode.
Seems pretty basic, anyone else have additional tips for a noob?
Tourguide in the file name
You need to have tourguide be part of the filename for the mp3 or it won't work. I haven't experimented with all the options yet, but I think it can be anywhere in the filename.