polymorphic associations

If i have the string 'us_address' how can I use that to create an instance for a view?

@us_address = UsAddress.new

Also, does anyone have a URL for how to construct forms for use with polymorphic associations? Everything I've seen up to now only shows the model relationships. How do you prepare to use this association in a form? What's the best way to know what partial to load based on what model a particular association will use?

I need to use multiple address types, us, eu, etc.


Some peeps from IRC helped me with this yesterday, so for posterity:

@address_type = 'us_address'

@address = @address_type.camelize.constantize.new