First of all I found an interesting Q&A up on the official site:

How many weapons or equipment can Altair carry at once?
There are four main types of weapons which Altair will be able to use in Assassin’s Creed – a long sword, short sword, throwing knives, and his hidden blade. The long sword is the medieval weapon of choice and as you progress through the game you’ll be given the chance to get new, better swords. The short sword is a traditional Arabic weapon and very good at close combat.

Throwing knives are clearly best for killing at a distance but these are consumable so you’ll have to think about when and where to use them. One of the main strengths of the knives are that they can kill with one hit, so you may wish to use them when surrounded by enemies but their key strength is in taking our archers when approaching your main target. Guards and archers that you kill around your target's lair will not be replaced so a good way to set up a successful mission is to sneak around and clear the area of as many soldiers as possible. You obviously also have the option to use your fists but hand to hand combat is only really useful when you want to get information from someone who is not wielding a weapon.

Last but not least is Altair's signature weapon: the hidden blade. This is a retractable blade attached at the forearm that juts out where Altair’s left ring finger used to be. You can use your hidden blade in combat but its real purpose is assassination. All of the spectacular and stealth assassination moves are available only when the hidden blade is selected.

Will Altair be able to use two weapons simultaneously?
Yes, you can use the short sword and throwing knives together.

Will Altair use poison to kill targets?
No, that’s not the way of the assassin. Historically assassins had to kill their target in plain sight and in front of large crowds. For many reasons (including gameplay) we didn’t want the assassin to be able to perform anonymous assassinations.

Will the game be localized in all countries?
Assassin’s Creed will be fully localized in English, German, French, Italian, Spanish, Japanese and Korean.

What role does the falcon play in the game?
For many reasons there’s a metaphorical resemblance between Altair and this well known bird of prey: our hero, like an eagle/a falcon, will hunt his target down, observe his every move, then strike with a single killing blow. He is always in control, analyzing his environment so he can choose the best possible course of action, all the while he keeps an incredibly low profile. And like a falcon, Altair’s outfit resembles it aesthetically. His hood was designed like the beak of an eagle while his cape was inspired by its wings. Also, when Altair performs certain acrobatics, to give him a feeling of weightlessness, his cape deploys itself like the wings of an eagle.

Will characters have an info screen (as in Morrowind) in order to see if NPCs are good or bad?
Assassins were highly trained not only in the physical arts like acrobatics and fighting but also in the psychological arts of reading people and social situations. Your Eagle Vision will be able to highlight specific areas of interest in your surroundings and when you are fully in sync with Altair you can use this to read the crowd and see who is against you and who is on your side. Depending on how they feel towards you, the NPC’s will appear in different colours – people who help you will appear in a positive colour whilst guards who are actively searching for you will be bright red. It serves as a social map that you can use to anticipate the crowd’s reaction.

Will Altair be able to store equipment? Example: Use a treasure chest or a leather bag?
The only pieces of equipment you can store are your throwing knives; Assassin’s Creed is not a RPG but more an action adventure game with a level up system – every time you rank up, equipment is restored to you. Sometimes it’s a new weapon that changes the dynamic of fights, like throwing knives that let you dispatch of enemies at a distance. Other times you get items that change the way you are able to interact with your environment.

For example, at Rank 4 you obtain a pair of Gloves which give you better grasping ability. This completely changes climbing and free running because you can descend buildings quickly by letting go and then grabbing back on. When you jump towards an edge your new gloves allow you to reach and grab on to things that were previously out of reach, and if you are falling because you have been hit by an arrow or other projectile, you can grab onto something before you plummet to your death. Other items like boots and special belts allow you to interact with the crowd in new ways. Ranking up is more then just getting a sword that does more damage – it changes your gameplay.

But I also found some interesting pictures showing some pretty neat gameplay mechanics....

(click for full images) 

You can find this stuff and a lot more on the official forum for the game.