Mine does the same - turn on a light above the keyboard and the ALS will shut off the keyboard light. Unfortunately, the drivers won't let you shut it off manually.
I can use the keyboard dimming keys (top row on keyboard) to turn it off on my MBP unibody running XP Bootcamp....check the Bootcamp settings in XP to make sure you don't have the setting "Use as regular F1, F2 Style" turned on.