The wii will definitely pass the sales of the PS2.
PS2 sales - Max 150 million - Probably 135-140 mil.
Wii is currently selling 1.8 mil/month = 21.6 mil/year
Historically the most popular console gains momentum in the 2nd thru 5th years.
It is likely that by the end of this year they will be selling 2.5 mil/month = 30 mil/year
By the end of year 5 this would make it 32 mil (Currently 21 mil + 1.8 for 6 month) + 30*3 = 122 mil.
By this time Nintendo will be introducing the Wii2, but with the large library of games and very low price (probably $99) they will continue to sell and ultimately pass the lifetime sales of the PS2.