its just too hard to predict right now, too many variables involved.

there are too many uncertainty here.
1. is the xbox 360 selling at the mass market price??
2. how many people are willing to pay current xbox price to play just one game?($60 a game is expensive)
3. how large the percentage of the current user base will buy halo??(the larger the percentage the smaller it'll move systems)

When Halo 3 is released we can observe if an old time mega hit can move next generation(ps3/360:high price system) in massive numbers, I bet most 3rd parties developer is watching very carefully on Halo 3's release outcome.

Halo 3 definitely will boost hardware sales, but for how many is hard to predict with so many just released great titles out and cant boost a decent increase in hardware sales.

I dont think Nintendo will be #1 for good, this war is not over yet.  Developers still havent announce any high profile projects for the wii, so far is only a few decent title is announce for it in the future(2008).  The Wii low end technology is another constraint for nintendo, even if ps3 failed to sell this holiday season, developer cant port their games to the wii because of its low end technology.  The end result developer will do multiplatform to xbox360.  Its always cheaper to port a game that build a new game from scratch.

 Outsell the Wii in October? No don't think so; even if it does, November and December belong to Nintendo.

Barely anyone on this site has been predicting Halo 3 will make the 360 retake the lead, especially during the last few weeks. The general consensus (if we ever have those really) has been that sales will definitely increase, but the distance will be too large by then.

Japan likely kills any chance of the 360 ever retaking the lead.

I really don't think so about Mario Galaxy: you forget that only half of the past Gamecube owners (people we could call "Nintendo loyalists") have a Wii yet: nearly 12 millions Wii's worldwide vs 24 millions Gamecubes worldwide, still a long way to go, just to have the same userbase... and that's without counting the millions of "newcomers"...

And if you look at the worldwide sales of "New Super Mario Bros", well it's more than 10 millions: i really don't think all these Mario fans have already bought a Wii... maybe half of them, maybe... and i don't even mention all the people who've played the NES Mario Bros, and could buy that "great new Mario" for themselves, or for their kids...

So, Galaxy has the potential to increase the Wii userbase by millions... it will all depend on Nintendo's ability to produce way more for the holiday season... but if millions of Wii's are on the market, they will sell like crazy, and many, many people will buy Galaxy as well... 

The major difference here is that Halo fans have an insentive to get an Xbox 360 now because there are actually really good games on it that would appeal to the FPS and Halo fans.

With Mario, Final Fantasy or Metal Gear Solid fans holding off, that would be because there are no other games that cater to this type of game format on these consoles hense there would be no point in purchasing until their game comes out.

On that note, I'm gonna take a long shot guess and say that During the Halo 3 launch week, The 360 still wont be able to overtake the Wii sales even just taking US into concideration.

Nice to have at least one who thinks it's not over yet. (Although I personally doubt that the 360 or PS3 still have a chance to catch the wii).

It's true that a lot of multiplatformers are / will be only available on 360 and PS3 BUT:

As you can see with a lot of already released 360/PS3 multiplatformers, they're ported from the 360 to the PS3 often resulting in a horrible framerate on PS3. If this doesn't change soon, then I don't see this as an advantage of the PS3.

Apart from that:

Many think that Nintendos system sellers are or will be Mario/MarioKart/SSBM/Zelda etc.

I don't think so. Most of the people who like Nintendo 1st party games (like me) already own a wii. The massive system sellers will be things like Wii Fit which will probably sell millions of wiis to people who barely know what a console is.

while i do agree that the wii is almost certainly staying at the top for good now, there could be a shock spike is 360 sales from all the 360 owners that have been banned from live wanting to play halo online.

My younger brothers friend had a 360 which was banned and he wasnt too bothered but he has just gone out and bought another machine so he can play Halo3 online when its released.
I doubt this will be comin place as he was a very big halo1/2 fan, but i think it could be a factor, especially with the massive amount of machines MS banned a while ago.

If the sales spike does push it in front of the wii, it wont be there for long, a few weeks at best. After christmas i think the lead will be far to vast for MS to ever have a hope of catching up, the only battle left will be if MS can fend of the PS3.

It will be close, but regardless of outcome, Halo 3 will be the closest the 360 ever comes to taking back the title for the duration of the generation.