Has_and_belongs_to_many UI help

Hi All,

I have a set up like this:

class blog
has_and_belongs_to_many :categories
end

class categories
has_and_belongs_to_many :blogs
end

I have created an intersect/join table like this:

blogs_categories

What I would like to do is create a UI where the user can select which
category a blog falls into (allowing multiple selection). Does Rails
provide any form of helpers to do this, or do I have to loop through
each category and add say a checkbox etc?

Thanks.