Sorry to hear that

. Without the original source code, reverse engineering the game will likely be nigh-impossible. It'll probably be much easier to just write an identical game from scratch. For good resources on Pocket PC development, check out the
Aximsite Developers Corner and
PocketMatrix Forums, among other resources. A lot of game developers, including Dan East (guy who ported Quake to PPC), frequent PocketMatrix. Good luck! :)
alan