Nope. Wii is still selling strong around the 80-90K range. 360 may outsell it for a short period but until the Wii loses some momentum it will stay in first. 360 may even have better Xmas sales (as it did last year), but Wii will still be ahead going into 2008.

Not sure if this has been addressed but your example of Halo 2's minimal boost of sales is a bit flawed. Halo 2 was released near the end of the Xbox's life and was not the first of the series to be released on the console. Many people wanting to play Halo 2 already had their Xbox because of the original Halo. There may be a significant number of people who have waited to purchase a 360 until Halo 3's release. Those who waited made the smart move because now they can purchase the revised hardware at the discounted price.
Whether it will happen, I'm not sure. I think the Wii may also rise in average sales with MP3's release if Nintendo has more out there so the distance may be even larger than you give.

If the 360 can possibly find a way to pull back ahead of the Wii in the future it won't be because of Halo 3. It'll be after a price cut or two, and big original games like Bioshock give the system farther boosts. 2008 could possibly be the big year for the 360 if things go just right for them. However for this year the 360 has no chance to retake the lead, absolutely none. Even in the US it'll probably only get a few weeks with 360 barely ahead of the Wii, than fall back in weekly sales for the rest of the year. In Europe I don't see the 360 passing the Wii for a single week, and we're all aware of that Japanese gap.

If the 360 wants any chance of reclaiming number one it has to do better with casual gamers and younger gamers where the Wii is absolutely destroying them. Halo 3 will have little effect on either demographic. It's a game playing to the 360 masses for the most part.

I don't think Halo 3 will move as many consoles as Halo 2 did.  There are several reasons for this:

(1) There have already been many top FPS games on the 360.

(2) The 360, as you mentioned, is far, far more expensive than the original Xbox was during Halo 2's release. 

(3) The 360 has a lot of negative publicity right now.

As people have pointed out, don't expect Halo 3 to work a miracle and move an unprecidented number of units (the number required to catch the Wii).  More realistically, it will move some 360s but it won't move any huge impressive number of units unless Microsoft comes out with some sort of great deal (similar to their $100 rebate last Christmas).

You never know....the most consoles I can see Halo3 adding to the already 10mil.+ would probably be around 2 million consoles (In its lifetime) just because the majority of the 360 fans already bought 360 Pro's, Elites and even that Core console already just for that game. Will 360 catch the Wii........I doubt it because Nintendo's "Halo Killer" comes out next week, which'll boost sales even more. Combine that with the already great sales of the Wii, by the time Halo 3 comes out, the Wii will be ahead 750k-1m consoles and still pulling strong while the 360'll just start pushing out normal Wii-like sales per month. Well there's my input to this discussion.

I think chances are quite high that X360 will pass the Wii for a short time just after the release of Halo 3. But with the release of Metroid prime 3... Wii will see a pre-holiday boost on top of a great season. And after Halo 3 come Super smash bros: Brawl (about as big as Halo in terms of sales) and Super mario Galaxy (potentially bigger) and Mario kart (almost same... ~7 mil). So... Maybe, yes. But for a short time cuzz Nintendo is firing their big guns this holiday seasons. And hell, are they big ones!

You can't quite use the numbers for halo 2 as a guide for xbox sales though. Most people who bought halo 2 would have also bought halo. Whereas halo 3 is the very first halo game on 360. I imagine more people will have been waiting for it.

Will the 360 regain the lead? That's a tough one. I think the wii is going to see a pretty considerable sales boost. Europe has super paper mario and my sims coming out before halo 3. Japan has mario strikers charged. America has my sims, metroid and a dance dance game.

I do think people are under estimating halo 3's impact though. There have been 6.75million 360's sold in america so far. Halo 2 sold 6.48million copies there, so unless every single 360 sale has been to a halo fan there are still a lot of sales left. Polls have shown that quite a lot of 360 owners aren't people who owned an original xbox. So I think there are still a considerable amount of halo fans waiting to buy the 360.

Working at Gamestop, I've taken some stats of my own. Here's what I've discovered;

94% of people reserving Halo 3 already have a 360. Therefore, it's expected to move some, but mostly it'll just satisfy the existing userbase.

The numbers just don't work out for the 360 to have a shot at overtaking the Wii again anytime soon. If it were next week it would be a much better chance. But when you are talking about a console having to more than double in sales just to stop losing ground...well at that point you are really moving far beyond the current precedent. As far as I know there isn't an example of a system selling near the 360's levels being doubled or tripled by the release of a game.

My best case 360 scenario for Halo 3 release:

Edit: Replaced my wall of text with a much easier to understand table.

So in that wall of text above you can see that even with the 360 sales tripling and staying tripled for more than 7 weeks it still doesn't catch the Wii. The answer to the thread title is simply a "no".

Maybe Halo 3 will hava an absolute insane attatch rate in america 95% then it won't move that many consoles if not it will move a quite lot