Is it possible to replace the harddrive? If so, I got a few questions. 1) It has the slow 60gig 4200, will getting the 60gig 7200 be worth it? Or should I get a 5400 unit? 2) How badly will this cut into battery life? I still want to be able to play movies on this unit. Needs to last at least 2hours playing a dvd. 3) Is the Harddrive user replacable? Uses the standard laptop harddrives?