Hi there, your questions are a bit too broad to answer on a reply like this. Here's the info that you should have:
Work experience: You don't absolutely need to have work experience, but you need to have very adequate reasons for NOT HAVING worked after college. If you're planning to jump into b-school directly after you graduate from college, you need to have substantial work experience and leadership responsibilities during your undergrad.
When to take GMAT: take it whenever you feel you're ready. Appearing for GMAT in January of 2012 means that you will probably be applying for round 3, which typically has a deadline around March (round 2 typically has a deadline in mid-January). I'm assuming you don't want to study for GMAT while prepping your application, since that's generally speaking a no-no. So if you plan to apply earlier than round 3 (which I do suggest you do), I'd aim for a GMAT appearance sometime in October/November timeframe.