Rails - Dec 2005 - Using Aggregations in HTML forms?

I am slightly struggling to get a basic aggregation setup

For example I have a column in my database called "email" which stores
an email address.  For various reasons I want the form on screen to be 
like "<enter email name here>@domain.com", ie the domain part is
already
fixed - the username is changeable

So I create a class called Email which picks the two pieces apart. 

class Email
    attr_reader :name
    attr_reader :domain
   
    def initialise(email)
        @name = ''abc''       
        #[@name,@domain] = email_addr.split(/@/)
    end
   
    def email
        return @name + ''@'' + @domain
    end
end

Add a "composed_of :email" to my main class.

However, when I try to add a field to my form like this:
<%= text_field ''mailbox'', ''email.name''
%>

I get an error:

|undefined method `email.name'' for #<Mailbox:0x37a1eb8>|


What am I missing?

Presumably this now complicates the Edit action because you can''t just 
assign the post results to the original object, instead you need to pick 
apart some of the results, turn those into a new object and assign them 
specifically to the correct fields?  Are there some common idioms which 
are useful here?

Is there a better way to do this?  Seems to me that I might just create 
attrs email_name and email_name= and then I can connect them directly to 
the field in the form?  Is this a bad idea?

Ed W