Enrolment

I'm running 1.8 Moodle on my server. It's LDAP-connected, so I've got about 300-400 users in my DB. I have a course (not metacourse), that is set as a course with guest accessability. But autorised users can't run quiz modules, cause they aren't enroled into the course. There are no users in "student" global site policy. When I enter the course as a student - I don't see the "Would you like to enrol into the course" words. So I can't enrol into the course and can't pass a test. Enrolment is "on" in the course. I've tried to remove user from the course and enter the course as a user, but I still don't recieve the enrolment proposial.
Should I add all students in my Moodle to the "student" category? I've got about 250-350 users as students, it's very difficult to sort them and enrol them into the course one by one. What should I do, if I don't want to add all users to "student" category and don't want enrol all users to the course, but I want all users to have possibility to pass quiz?