Nintendo has won the handheld war, but how the PSP ultimately fairs is up in the air. I think Sony has to be satisfied if it can stay on track as do half what the DS does. However since the Lite has come out the DS has done better than 2 to 1 over the PSP in virtually every market. Unless the price cut, or a soon to be released PSP Lite, makes a big difference, than I see the PSP ultimately selling only 30-40% of what the DS does world wide. The DS is a monster right that can't be stopped.
However the PSP will be very successful. I'm predicting a 40-50 million sell through rate for it, and while it won't look like much compared to the 100-120 million the DS sells it still will set up another interesting, and potentially more competitive, battle between the PSP2 and Nintendo's next handheld.