Yes they are backward compatable. Keep in mind your computer will only run as fast as its slowest component. So while your mb w/ 1600 FSB is compatable w/ a 1333 cpu, your computer will only run at 1333. So i usually suggest matching one with the other, why spend more on a cpu/mb/ram when it will only run as fast as the slowest component. Make sense?
I usually suggest trying to match FSB of all parts whenever possible, while they will still work you will be cutting the lifespan of the parts down - since it is more stressful.