Client Access permission public folders???

Hey MX gurus

We have our exchange server 2003 and I am setting permissions
to who can access these publics and how they can access them..

I am confused...you can right click on our resource groups and it says "Add public folder"....this seems to automatically fill in the Member Of tab when you right click on the public folder..okay so to me this is setting NTFS permissions right? I was told by a vendor tech that this is for you to tie a mail distirbution group only to the public folder and he showed us this way to assign permisisons via client permissions on the public folders property tab that to me is unorthidoxed? How do you set client permissions on the public folder? can't you do it thru the Member of tab???
and or right click on the resource group????

thanks for your help..