I get this periodically where my 2007 MB forces me to restart... I haven't been able to identify and specific tasks that causes it. It seems to happen most often shortly after starting up. It usually takes 3-4 restarts before it stops. I'm running 10.5.8 on a 2007 MB 2.2Ghz w/2gb RAM. 2 things that it could be related to in my amateur opinion is either the RAM or Battery. The reason I think one of those 2 could be the problem is that I put the RAM in a 2006 MB as well as the battery and it came up on that machine as well... Anyone have any experience with this problem?