Got this one working too.
PacMan Score Maximizer: Download
Rehash & resign with YOUR ID's
Code:Mods High Score to 99999999 This is for the XBLA original PAC-MAN game.
How to Use:
1) Extract savegame.bin from your save.
2) Open in this editor
3) Maximize your score
5) Rehash & Resign with Horizon