validation & errors

OK - now that I have written validations for my activeldap models and check them before attempting to save so I can provide normal language error messages to users by using @MODEL.validate? and setting flash[:error] with @MODEL.validate before rendering edit/new screen again.

I find that what I lost was the nice .field_with_errors 'class' apparently automatically generated with errors (seems to be a new Rails 3.1 thing but perhaps it was there in Rails 2.x and I never actually noticed)

Is there some way I can essentially duplicate and get the errors from a save without actually calling

Bonus question along the same lines... If I have a input field that is say a collection and is not the actual stored field but rather one whose data is processed into the ActiveModel saved record before saving, can I assign the error to that field somehow?