I find examples and tutorials about models and about validation. And I places that say the validation (or most of it at least) should be in the model, which I agree with. But I
I have a brief write up with how to handle this at the link below since it took me a while to figure out and I couldn't find a single good example.
http://www.matt-toigo.com/dev/orm_with_validation_in_kohana_3