you can't really force anyone to play a spellcaster. Often in my groups games thier isn't a pure spellcaster or healer. Basicly what i do is give them lots of healing supplies and just custom tailor the adventures so that they can succed without a spellcaster.
If your really intrested in getting them into playing spellcasters i would suggest a class like warmage, dread necromancer, sorcerer or warlock. Very little book keeping needed with these class's , no spell research needed for the most part and they will get to see how powerful magic using class's can be without having to do thier homework