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MIT OpenCourseWare does not offer standard, traditional courses. They are basically archived classes which were taught to enrolled MIT students, the archives now being free and open to the public. You can see various materials from these classes and work through them for your own intellectual benefit, but you cannot register for the class or take it for any sort of certification.
You should look into the EdX initiative - www.edx.org - of which MIT is part, in collaboration with some other schools. They do offer free online classes, not for college credit but for less formal certification. And these classes are close parallels of the courses these schools offer to their enrolled students.
Another terrific resource for similar classes is www.coursera.org. They have more classes than EdX, though in my personal and unofficial opinion, I prefer the quality of the EdX classes more.
Best of luck to you.