But there are LOTS of types of AA. PROPER (the best) AA is ONLY possible on XBox due to memory constraints (it has 64Mb of VRAM compared to GCN's 24Mb). It's called subpixel anti-aliasing, and it means that the frame is rendered at a very high resolution (say, 1600x1200) in the frame buffer, but then it is, for want of a better word, squished down to 640x480. There is no MAGICAL way to do this on the GCN, you NEED a lot of VRAM. There are, however, other types of AA (interlaced, for example) and there are ways it can appear to have AA (blurred screen etc.).
But, XBox (as much as we don't want to admit it) is CERTAINLY the most powerful of the three consoles out right now. There are things that developers can do with its Pixel Shaders that the other consoles can't get close to (even the PS2, with VU0 and VU1).
The textures in MGS3 are FINE. I don't know what you're all getting so worked up about.
And there is one LARGE reason why I don't think TTS will be as good as MGS1 - the WOW! factor. Sure, TTS is practically garunteed to be a very good game, but it CANT have that little bit more that puts it as an all-time classic (the story, for example).