From what i believe firstly mamece runs a fair few .36 mame games. Megamamece runs many many more .36 mame roms.

Firstly if you go to one of the drop down menus (dont have my PPC to hand) you should be able to select 'view all available games' or something like that. It'll then display 100's of names on your PPC. These are games which will work with Mame thats all, its just a list not a list of games installed on your PPC instantly.

The games should be in the ROMs directory kept in their zip format.

Email me (psj3809@hotmail.com) and i can email u a few roms to test to make sure Megamamece is working 100%. The black screen you have i presume is for the wrong version of roms as it should come up with 'press OK' etc