Depending on supply Nintendo could take a big chunk out of that goal in November and December being that they are (practically) ensured of outselling the XBox 360 and PS3 combined on a worldwide basis over the Christmas period.
I'm (personally) anticipating that the holidays (Thanksgiving [US] and Christmas/Hanukkah [wordwide]) will cause a spike of interest in the Wii because a lot of people who have never been exposed to it will go to their friends/families houses and end up playing some Wii Sports. I can imagine that the Wii could see 'Christmas Level' sales in January (and possibly February) even without any major game releases.
If Wii Fit takes off in Japan it will get the greatest 'Free' marketing campaign when it is released in North America because it will be covered on every major network on the news and in shows like Dateline and 20/20; it works as a general interest story and can tie-in well with new-years weight loss programs and child obesity news stories.
If everything goes well for Nintendo I would say they will pass the 360 and PS3 combined by March 31st 2008 but I personally wouldn't expect it until September 31 2008.











