I don't think there is *any* chance either console will reach 20mill by the end of the year (i.e. Xmas 07).
Even if Ninty manage to manufacture/sell 10m units in the next 8 months - that leaves the 3-4m short. And making 10m in 8months is no easy feat.
Following traditional sales curves (and assuming the PS3 doesn't steal the 360 thunder) the 360 will sell another 5-7m units this year - giving it a global base of about 15m-17m.
The Wii may (or may not) exceed the 360 by Xmas - its completely dependant on Nintendo's ability to increase production ASAP (to some huge level). Find out in 2 weeks what their projections for the next 12 months are.