Deny insert/delete for all users in SQL Server 2005
It would be confusing if you granted someone db_datawriter and then denied them delete rights.  So if you can, remove them from the db_datawriter and then grant them the rights they need:

create role role_MyApp
grant select, insert on Table1 to role_MyApp
...
exec sp_adduserrole 'role_MyApp, 'User1'