Yes you can polish a new car. In fact after I polished my 1 week old car, the paint looked alot better than when I started. Remember, polishing is not really to remove scratch marks, it's to really "clean" the paint and remove ever so slight imperfections so that you can apply a wax/sealer.
So the procedure spelled out in the thread I reverenced is still valid. Also, before you dive in and get a PC, I would suggest you check out: http://autopia.org/
. They have answers to all of your questions in either FAQs or in the discussions (just use the search feature). I got ALOT of info from that site before I starting doing anything on my car.