i look at it this way...if halo could only put a small dent in the jugernaut of NIN then GTA4 will not even leave a smear on the Wii roller

I think the answer to this question lies within the PS2 install base within North America. The Grand Theft Auto series has a greater brand recognition then Brawl. Perhaps only due to the exposure. Needless to say if someone has played and enjoyed Grand Theft Auto, and has never played Smash Brothers. Then for them the high definition consoles will be more attractive. Given the 360s previous library offerings, and the lower price the majority of the attention will go to the 360.

I strongly believe that Smash Brothers is dramatically over estimated and Grand Theft Auto is dramatically unappreciated. I think if Microsoft advertises correctly, provides another price cut it needs to get into the mainstream, and this Grand Theft Auto is highly praised within the press. Then yes this title could thwart Nintendo for a couple months. The only real consideration is whether Microsoft will play their cards perfectly, and whether they will continue high quality delivery in the short term.

I think Microsoft would do well for their console if they also advertised many of their older titles again to strengthen the perception of their library. During Grand Theft Autos launch week. Perception is a strong component of the battle.

Can I borrow your crystal ball?

 Not sure where your coming from.  But given the reasons I stated I directly answered the question: Can GTAIV Stop Wii from Catching Xbox 360 in the Americas ?

with:

 No chance.

The only thing that can save MS from being past in June is an insufficient number of Wiis in stores.

^ i am not saying the game wont sell well but look at what halo did in its debut....all nin had to do was flod the market with wiis and it only just got beat

I don't think it will stop it, but it very well could delay it for a while. There are too many variables for me to try and make any solid predictions. Will wii get supply issues for the US under control? Will the 360 get a price drop? How hard is sony going to be advertising GTAIV compared to microsoft? Exactly what is the exlusive content microsoft bought?

I'm just not sure. When GTAIV comes out it will definately give MS a big boost, but how big and for how long I'm not sure. And who knows what's up with the wii.