A friend of mine had a similar problem with an iBook. There would just be a hard freeze, especially when printing. I'm not exactly sure what the particular problem was, but it was obvious that, after 3 reformats & installs, it was a hardware problem. Your best bet is to take it in while you are still under warranty and get a new logic board. I found that you have to be pretty tough with Apple support because they are quick to jump to conclusions. They try every software thing, and it just doesn't work. So, I'd call them and firmly tell them your problem. They will probably install a new logic board. Good Luck!