[dba-SQLServer] Read only rights

I created two users to test the rights I assigned and how they function, straight in SQL Server. 
One is read and one is read and write.

The read / write operates as expected, however the read only allowed me to modify but not save the 
modifications.  Somehow I expected the query to be readonly.

Again this was directly in a SQL Server table, logged in to SSMS through that user.

I expect the same results once I get to getting at the data from Access.  Is there a way to prevent 
even the appearance of modifying the data if the user is read only?

-- 
John W. Colby
www.ColbyConsulting.com