Vista - Read Only Property

I have a data access layer, which maps on to my tables on a 1 to 1 basis. I
have a class for each table with New, Update and Insert method and a
corresponding class for collections of the class. I want to make some of the
properties readonly unless the property is created as part of a collection
(in the corresponding class). Is this possible.

Basically the main class is based on a view so I want any lookup table
fields to be readonly. However when I create my class as part of creating a
collection I can't write to the property.

Regards, Chris.