Under CentOS 5.2, is it possible to mount an iscsi filesystem/partition as rw for root, but ro for users?
Possibly, but iSCSI is not a file sharing protocol. You can only mount cluster FS's with multiple ini's or when root changes the FS while another client has it mounted funny stuff happens such as ro clients not seeing changes etc.
iSCSI is not designed to be used in this fashion.
jlc