Ok, as the second founding member and lead programmer of JEPE, I decided to answer some questions too.
As for why we're using XML: listen to Bonzai. The first version used 2-dimensional arrays, but that's not something you can write by hand easily, so I thought XML would be better.
@Zerro: great! Thanks man. The best way to help us is to help us with writing the engine, or to submit ideas for file formats to manage the pokémon data, item data, move data and ability data. I'm currently working on finishing the mapping language now, so other people can start mapping, write editors and help me with the parser. If you'd like to write the specs for another file format, it would be nice to do it in a similar way. Unfinished documents can be found here: h ttp://jepe.ptreasures.net/documents/ (remove the space)