Can you post a few details of the hardware and software configuration, and please post the full text of the reboot message and any error message(s) that you're receiving?
Do you get any time before the restart request to issue commands or related, or is the system booting and then requesting restart?
Your footer indicates a MacBook and OS X 10.6.1, though 10.6.8 is the last version of OS X and OS X Server in that Snow Leopard series. (OS X Server isn't commonly installed on nor used used on a MacBook, either — that combination wasn't supported AFAIK. OS X client would be far more common on a MacBook or MacBook Pro. OS X Server is somewhat more complex than OS X client software, but neither are usually requesting looping reboots, save for a very few cases where system firmware needs to be installed, or similar low-level steps.)