is Mickey's Magic Mirrors worth to rent, I hope they make Kingdom Hearts for Gamecube, that game looks awsome.
Mickey's Magic Mirror is a good rental and a good purchase for younger gamers. It's mostly an old-style adventure game in the vein of Monkey Island or Maniac Mansion (only toned down in difficulty and complexity).
Kingdom Hearts is only coming out for the PS2 and is not slated to be released on any other systems or the PC. I asked my contact at Square and she said there are no plans for any type of port. I also think the newest OPM (with KH on the cover) has the director of the game quoted as hinting that there will be no ports.
The only talks going on about the future of the KH franchise is that there may be either a cartoon series, movie (direct to video most likely), or amusment park attraction based on the game. There is also a line of KH toys coming out later this year.
As for the Square/Nintendo thing, you are correct in a way - but not 100%. True there is a Final Fantasy game coming out for Gamecube, but it's not in 'THE' Final Fantasy (meaning Final Fantasy I, II,...X) series. Instead it's called Crystal Cronicle and is based mostly on the Japanese Final Fantasy television series.
This is being developed by a studio that is an off-shoot of Square that is being funded by Nintendo.
Final Fantasy XII (which is the next Final Fantasy after XI) will be released on the PS2 since Sony now owns part of Square.