(1) A good way to have a reliable backup available is to purchase a FireWire external drive and download Carbon Copy Cloner. Set CCC make a copy every night while you are asleep. Of course disks crash so its probably good to burn a few CD's as extra backup, store off site etc etc.

If you find your mac won't boot one day you can startup with the Option key down and then boot from the FW drive. Then its time to find your copy of DiskWarrior.

(2) If you mac is turned off or asleep at night you probably should run MacJanitor every now and again.

Someone else with more expertise than me might like to advise if (2) is really necessary.

Michael