Dagon is right. Mysqldump is pretty amazing. All you'd need to do is determine what your mysqldump command should be (try experimenting a bit in a terminal window -- you might have to specify a user/pass, etc.) and then you can just create a cron job to run that mysql command. I would recommend dumping the DB to a separate hard drive if you can. In my experience, hard drive failure has been the main reason for data loss.
