How to clone a linux hard drive

Well, I just want to know if there is a proccedure, command or program to clone a hard drive with linux OS, (RH8).
The other day, I was able to clone my old win98SE with great results, just to backup enterily my HD.
Look, 4 or 5 months ago, I switched to linux OS; I have been downloading and installing a lot of updates!! but I’m affraid some day I will make a mistake, even not running my computer as root.
Can you help me? (of course, I’m a newbie)