Hmm, that’s a handy piece of software.
I’ve just had a play with it using TomTom on a PDA so this may be different for you, but if you save each category (ie stone circles) from Google Earth instead of the whole file, then open them in Tyre and save as individual POI files on your device then hopefully it should work ok (it does on a pda anyway). It’s also possible to associate a small bmp icon with each category too. Hope that helps.
-Chris