I did a clean install of Tiger on my PB (15", 1.67GHz) last week, and my machine halted occasionally. I couldn't capture the screen (since the system died) but it showed messages like "You have to restart your computer. Press restart or hold power button for several seconds... " in 4 or 5 languages (English, Japanese, etc). It happened when I was watching vedio files, tranferring data between my PB and external HD, and even making a DVD image. Does anyone get the same problem? Is this because my HD overheats? I've never had this problem until I installed Tiger. Much thanks.