I think Disk Copy is more like Drive Image, and you don't have to buy it because it comes with every Mac

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You can either run Disk Copy from the CD that came with your computer, or your hard drive. It does exactly what Drive Image does, it makes a file with an "image" of your hard drive. You can put the file wherever you want.
Retrospect is a bit more advanced. It automatically makes daily, weekly, or monthly backups of your whole drive, or just a certain folder. You can back up to whatever media you want (assuming it your data will fit), and I'm pretty sure it also lets you save it as a file on your hard drive.
I would burn a CD with a copy of Retrospect (or Disk Copy, depending on what you use) and a system folder, so you can boot from it when you need to restore your data.