Assuming you use Windows Xp, you can setup an automated backup to execute at a time you choose daily and backup to the hard drive. Just goto start, run, type in ntbackup, press enter. Or you can find it in start, programs, accessories, system tools, backup.
There's a wizard that'll walk you through selecting the files you need to backup.
There's other commercial apps that do this with a little more finesse, but Windows backup should work just fine.
For a full hard drive image, there's lots of freeware out there that'll do it for you.