You can put 'user' between the parameters in the specific fstab line. Like this:
/dev/hda1 / reiser4 auto,user,ro 1 1
That way a normal user can mount/umount partitions (or cd's and stuff). Also, when mounted at boot, a user should be able to umount it anyway. So I don't think mounting it as root will prohibit any user from unmounting it with the above option in the fstab - but I'm not 100% sure about that.