Users, Groups and Priveleges

Users, Groups and Priveleges I know I have asked this question before, but here goes. Without going into Unix (the Terminal)is there a way to have one Group of users access a directory/folder with Read/Write priveleges, while a different Group of Users have only Read priveleges to the same directory/folder. I know there is the Owner, Group and Everyone else and that I could set up a Group with Read/Write priveleges and Everyone else only Read priveleges, but I need to be more selective (Everyone should have no priveleges). Please help. Thanks.