Agree with beanie - J-Plan is good, runs on the Palm and uses a well proven Buhlman algorithm with tweakable GF's and can do Trimix and CCR diving. I know the guy who wrote it, and was using it until recently when my old Palm Vx died on me
Alternatively V-Planner uses the VPM-B algorithm, does Trimix and CCR, and is available for Pocket PC, but will cost you money.