Microsoft is one of the most sought after destination for most students wanting to pursue a career in the software industry. Microsoft is a very well known name and having been associated with it is always going to shine on your resume. Being associate with a company that is at the top of their game is also a big attraction for students who apply to Microsoft for internships.
Microsoft does advertise for any internship openings in their company. If you want to work with Microsoft it would be a good idea to start looking as early as possible. For a single internship available in Microsoft there are a lot of people who apply for it. If you are still far from reaching a stage where you could intern with Microsoft it might be a good idea to strengthen your resumes in the meanwhile. If you are able to undertake a project that is related to your profile it might ultimately help you. You could also pick up an extra-curricular activity that would enhance and develop your personality further. Such an experience always helps you. Companies like hiring interns who have a well rounded personality.