volume permission

hi as you can tell by my post count i'm new here and i'm also new to leopard server. i'm trying to set up a sftp server and i have most of it running but i'm having issues with permissions. i have two internal drives one being for os x server and the other to hold all the files. when i sign on with one of my users via transmit i can see both my os x drive and my files drive. i tried setting the os x drive permissions to type>deny permissions>full control but when i do that the user cannot log in at all even though the user is allowed access to the files drive. how can i deny access to system files but allow access to the files drive? thanks for any help you can give me, - tolva