We introduced a kitten to our household 2 years back and the established cat (who had always lived with another cat, her mother) took an instant dislike to him.
the vet suggested feeding them in seperate bowls and keeping them apart whilst he was young. (don't know how I didn't think of that myself, D'Oh!)
2 years later they tollerate each other amicably, although I don't think that they will ever get to the 'washing each other stage', Sox, the older one, rarely washes herself, so there's no chance that she'll do it for another cat!
Anyhooo, when Max was about 16 weeks old (or about that - I can't remember exactly) we took him to the vets and whipped his pride and joy's off and he instantly started to grow at a faster rate and is now as big as Sox who is 11 years old and weighs 13 lbs!!
Moral of the story; they get used to it!