Ok, lets look at this constructively. The PS2 will sell ~125 million from start of production to end of production. It is near the end of decline so sales will only decrease for the PS2 now.
We can tell that the DS has reached Maturity judging by sales in Japan and several other areas. So this means the DS can enjoy a period of good sales that will begin to decrease as Nintendo release information about the DS's successor (assuming this information will be released during 2008 and throughout 2009).
I will estimate sales until for 3 years, which by then the DS should have been succeeded...]
end of 2007: ~64,000,000
2008: This year
~425,000 sales per week
425,000 X 52 = 22,100,000
End of 2008 total (est) = 86,100,000
2009: Next year
Decline (est) 15%
425,000 X 0.85 = 382,500
382,500 X 52 = 19,890,000
End of 2009 total: 105,990,000
2010: People start to talk about DS successor
Decline (est) 25%
385,500 X 0.75 = 288,750
288,750 X 52 = 15,015,000
End of 2010: 121,005,000
Edit: title is supposed to read "Estimation the DS will beat world wide sales of PS2 by 2012"
2011: DS successor released
Decline 50%
288,750 X 0.50 = 144,375
144,375 X 52 = 7,507,500
121,005,500 + 7,507,500 = 128,513,000
End of 2011: 128,513,000
as you can see by my maths the Ds will beat the Ps2 sales at the end of 2011.
