Its still a bit early to know. The Wii has a lot of upside (huge potential for increase in sales for next 12 months), whereas PS2 sales will only weaken from here (I presumed you factored in increases in the PS2 install base).
Its going to be hard to know, and sort of irrelevant if/when it does happen (PS2 will be well and truly 'dusty' by then).
Gesta Non Verba
Nocturnal is helping companies get cheaper game ratings in Australia:
Wii code: 2263 4706 2910 1099