best thing to do is let your computer stay on all night, every night. it will run scripts on a daily, weekly and monthly basis to do much of what you're asking, but ONLY if the computer is on at like 2:00AM (or something)... and it has to be awake, not just asleep. if you turn your display to sleep after an hour, and your disks to spin down, it's virtually the same thing, except for fans. with panther, i think you can specify startup and shutdown times, so that would work as well...
pnw