I have a powerbook G4 and whenever i move the screen, the bottom half flashes. It is either black or white and sometimes it lasts for a second and other times longer. Whats wrong?!
Could just be a loose cable or such. No matter how careful you are, portables get shaken around quite a bit.
If its under a year old, its under warranty (even without purchasing AppleCare, which you should!), so it costs nothing to have them fix it up for you.