This is what I have heard thus far, and I have kept close tabs on info:

Advent Children will be released in Japan slated for Summer/Fall 2004, and a Winter 2004/2005 estimate in the States. Not a simultaneous release as originally hoped for.

It will be released as a DVD first in both Japan and America during these projected periods.

When the Playstation Portable(PSP) is eventually released, a UMD format disc containing the movie will be released shortly thereafter in both Japan and America as well.

The movie runs approximately 90 minutes.

The antagonists are three Sephiroth clones: Kadaj, Yazoo, and Loz. Kadaj and Yazoo are clearly clones of Sephiroth. Loz looks very different, but I am fairly certain he is a clone. Cloud didn't look too similar to Sephiroth now did he?

There is also a mysterious character in a wheelchair with a white cloak over his head, whom Kadaj appears to take orders from.......Sephiroth?

The three clones are trying to influence the children of Midgar to assist them in their evil scheme.

What this evil scheme is?

The movie takes place two years after the events of the game.

Cloud, Tifa, Barret, Red XIII, Vincent, Cid, Marlene, Reno, and Rude are all confirmed characters.

Reno and Rude will assist Cloud and friends in the fight against the clones. Wether they will be friendly or not, I cannot say.

Kadaj uses a long katana esque sword. Yazoo uses a small form of a gun sword. Loz uses some kind of "electrocution fist" type weapon. Cloud uses his Buster sword of course!

I am certain Kadaj can use some form of magic. I assume Yazoo, Cloud and such can use magic as well.

Last but not least.......this movie is going to rule the world!!!