Thanks for the senior members answering questions, so I'll just reiterate some of the answers.
The two multiplayer modes, Skirmish and MMO will be different. Skirmish will be a one time build and destroy battle with up to 8 players, your units will not carry on from Skirmish mode. MMO mode will offer a different style of play with PvP and PvE aspects, we will be releasing more info on the MMO aspect sooner to release.
The Xbox 360 version isn't going to be watered down at all. We are optimziing the Xbox 360 version to play just as good if not better than the PC version. You will be able to download any maps made from PC users, and will be able to download the Map Editor to create maps on your PC. (However the Map Editor requirements are identical to the requirements to run the PC game, so some people might not take advantage of this).
The game will be available for play on Windows XP. So far we are not optimizing for Direct X 10, so it wont be a Vista exclusive.
We are debating the possibility of a dragons and other objects causing death and damage. We think it is a good idea, however the amount of work to get that working in the game is considerable. So for the moment it's going to be put on the list of "add if we have time".
You can team up against CPU players, or just add them as other adversaries in Skirmish. MMO should feature some play against CPU opponents as well.
I answered the Xbox mod question earlier on, but yes you can download mods for your Xbox 360 game.
I personally haven't played BFME1 or 2, so I don't have an Idea what War of the Ring mode is.