virtual classroom

I want to build project with Drupal 6 here is the project details.

1) The system will be having 3 roles:
• Instructor
• Student
• Admin
2) Admin
• Managing user accounts, course registration approval
3) Teacher
• Login, Create / Modify course details, set Quizzes, assign grades, online lectures with whiteboard functionality
4) Student
• Login, Register / Unregister for courses, take quizzes, online lectures , view lectures in offline mode
5) Online whiteboard functionality.

Please help me, which modules should I use for above listed functionality.