I like the free demo of SuperDuperto make clones. It's free, Tiger&Leopard&Snow ready and is easy to use. If you buy the full version you can do incremental backups.
You should use Disk Utility to do a Disk Repair, as shown in this link, booted up on your install disk, before you make a clone of it.
I then partition my external disk, in Disk Utility, with a partition that is the same size , actually a tad bigger, as my system disk. I then use SuperDuper to clone my system disk over to that partition.
With a clone on an external FireWire drive (USB drives are not bootable on PPC Mac's but most are on Intel Mac's) you can bootup on it to do your repairs or just run your Mac anytime you have trouble with your main drive. Be careful, there are a few external FireWire drives out there that are not bootable on Macs. Check the drive's manual to be sure.
DALE