Here are some facts, rumours and unconfirmed news about the Square/Nintendo situation:

(last update: 27/3/2002)
FACTS (100% official)

- Square will release Game Boy Advance games through a game planning and developement company (called Game Designers Studios Inc), that will be leaded by Akiyoshi Kawazu (who worked on several Final Fantasy games). The first few games will be ports of popular Square games.

-The developement company will receive funds from a  financial fund called 'Fund Q', set up by  Hiroshi Yamauchi, president of Nintendo. The company will receive the investement to "develop a new type of game".

-A new Final Fantasy that supports the GC/GBA link will be released in time for christmas (in Japan).

-Square plans to release 3 to 4 GBA titles in 2002, one of them will be Final Fantasy Tactics.

- Final Fantasy Tactics is 30% complete and will be released this christmas. It will be based on the PSX version, but it won't be a straight port, nor a full sequel. One of the new additions is the ability to autosave. Read more about it
here (Madmans café)

-Square is still going to work on the PS2, in fact the PS2 will remain Square's main platform. Square  had an agreement with Sony  (the second major stockholder of Square) that the Square/Nintendo contract won't affect their support for the PS2.
UNCONFIRMED (likely, but still not officially announced)

-The first game from Square for the Gamecube and Game Boy Advance will be based on Final Fantasy Unlimited, an animé series. There will be made use of the connectivity between the GBA and GC. The games will be released (in Japan) towards the end of the year.

- Square will release multiple GBA games in 2002, probably ports of Final Fantasy V, VI and Chrono Trigger, and maybe other SNES RPGs.

-
Spong.com claims that the new Final Fantasy is tentatively called Final Fantasy N. It will be on GBA and GC. It will be the same game on both consoles, and the link feature is used. You will be able to play the game on GC, save your game on the GBA, and then continue your game on the GBA. Read more here.

RUMOURS (100% speculation)

- Game Designers Studios will do ports of Final Fantasy VII, VIII, IX and X for the Gamecube.

- Square will release the third Chrono game on Gamecube and GBA.

- Final Fantasy XI, the Massively Multiplayer Online RPG, will also be released on the Gamecube.

SQUARE AND NINTENDO BACK TOGETHER
special thanks to the following sites who helped me in making this feature: Madmans Café, Gamespot Japan and Planet Gamecube.