1st, sorry for my broken english , will improve this skill in near future.

Can anyone of my party members become (for example) an assassin or are only rogues(ninjas?) allowed to become an assassin?

Same: Wizards->Zenmaster

Cannot figure out this only by reading the book!

For the ones who finished the game:
How many time did you "waste" for (on?) this game?
I never before played a wizardry rpg ("only" might&magic).

MiMo

I played Wizardy 7 and my friends too, we think that Wizadry 7 was (is) the longest and toughest RPG. Many people end on some puzzle or too tough monsters and really only several people finished game (at least as I heard). Cannot tell about W&W, because I just started, so far looks like best RPG I played in years. Hardcore RPG. Serpent temple was very challenging like old good table AD&D. Most importantly, character development is great and complicated and that's what makes W&W and Wizardy so great games - Lotsa quests, spells, skills and option to develop your character (plus you have more than one

I think only the Rogue can become an assasine !
Because i tried to talk to the ratlings with other characters, but they didn't got the job from them...
I not completely sure....better to do a little testing on it !

Have fun with the game !