in enterprise manager you can add their AD user to the security for the server.
Then go to the database and right click the specific tables you want to give them rights to and select properties
On the page there is a permissions button you can give the users specific select/insert/delete rights
If you have at least sql 2000 you can create 'Roles' (aka groups).
You assign hte permissions on the tables by Roles, then add the users to the specific Role
ie if you want a reporting Role for your accounting people.
I never ever use the sa account, I only use trusted.
If I'm creating a website then I use sql server accounts that only have rights to specific tables.
You can also specify which columsn to give people rights to if you wish.