How do I assign an entire Active Directory group security access in SQL Server 2008?
Set the AD group as a login. And "login" means server level login not the AD concept of user/login. In SQL Server speak, this is a server level principal
Create a mapped user in. You shouldn't really permission a user directly on tables. And "user" means database user not the AD concept of user: in SQL Server speak, this is a "database level principal"
Add user to role (also a "database level principal")
GRANT permissions to the roles on the tables (a table or proc etc is a "securable")


Sample script

USE master;
GO
CREATE LOGIN [MYDOMAIN\APPLICATION SUPPORT] FROM WINDOWS;
GO
USE mydb;
GO
CREATE USER [MYDOMAIN\APPLICATION SUPPORT] FROM LOGIN [MYDOMAIN\APPLICATION SUPPORT];
GO
CREATE ROLE rSupport;
GO
EXEC sp_addrolemember 'rSupport', 'MYDOMAIN\APPLICATION SUPPORT';
GO
GRANT SELECT, INSERT,UPDATE, etc ON Mytable TO rSupport;
GO


sp_addrolemember is deprecated starting with SQL Server 2012, where ALTER ROLE should be used instead.