Um.. how does the multiclass function work in NWN? I made a barbarian who's pretty good with axes and ****.. If I were to multiclass, during the game, to a cleric - will I only be able to use clerical weapons then?? And will I still be able to advance in the Barbarian class? help plz

Your Barabarian will be the same, only with a level of Cleric.

There are no weapons restrictions is 3E, there are feats for proficiency in simple, martial and exotic weapons, and some classes get some of them for free.

You will still be able to advance in Barbarian as well. If Barbarian or Cleric is not your race's favored class, you should try to keep the levels within one of eachother so that you don't incur XP penalties.

It's like (a litle) 2E Dual classing, exept that all class has the same XP rate, you can "dual" any class, and you can advance in any class, oh and you do not need stats requirement (Though a cleric with 8 Wisdom is well... stupid) and having one level of X casting class do not give you acces to all the X class spell list, You get all of the class benefit not the "Best of" and a class is never "inactive", so if your a Barbarian 5/Cleric 7 then you have all of the benefit of being a Barbarain 5th level and a Cleric 7th level, Finaly at each level up you chooce wich class you want to level... Finaly it's sooooooooo not 2E dual classing eh! Hope That's help...

One other thing to mention about multiclassing is that the bonuses to hit and saving throws for each class stack together.