Yai! One more unfixable problem!
I did as you suggested.. and it worked fine. I merged another model hands, scaled them so that they stick to the finger bones and adjusted the arms. After the weighting, I saved and exported as a .xsi, deleting the caps and the cape.. just becouse I wanted to see how it would perform animations.
So I read your assimilate&carcass tutorials and set everything ok. I fixed the path in preferences, changed the numerical system to U.S and my keyboard settings... And, as I tried to compile the carcass, it gave me that fastidious error about "Cubic Scale Keys".
Dunno what to do..