This is not so difficult. I use tar for my routine backups on my systems. If I want to make a restore disk that includes several operating systems then I use a rescue cd distribution (System Rescue CD) and partimage.
Let's say that your system is installed on /dev/hda1 and you have an external hard disk on /dev/sda1. Let's also say that you already have a mount point at /mnt/backup and that you encrypted the external partition with True Crypt. This is what I do.
First I mount the external disk partition on /mnt/backup.
Second I make a backup of the system disk's Master Boot Record using dd. If you have logical partitions you will also need to use sfdisk, which I will include in my example. These copies of the MBR and partition table are written to the / directory in files named <date>-hda-mbr.dd and <date>-hda-partitions.sfdisk.
Third I use tar to make a backup of the / file system storing the archive file in /mnt/backup/<date>-rootfs.tgz, using the --one-file-system parameter to prevent tar from backing up the contents of /mnt/backup et. al.
truecrypt -t /dev/sda1 /mnt/backup
dd if=/dev/hda of=/`date +%F`-hda-mbr.dd bs=512 count=1 conv=notrunc,noerror
sfdisk -d /dev/hda > /`date +%F`-hda-partitions.sfdisk
tar czv --one-file-system f /mnt/backup/`date +%F`-rootfs.tgz /
Of course if you don't use True Crypt to encrypt /dev/sda1 then you can just mount that partition using the mount command.
Using partimage is also pretty easy. I boot a CD containing System Rescue CD. We need to do this because partimage won't back up a mounted partition/file system. Partimage is particularly good if you have a dual boot system and you just want to get a snapshot of your systems before viruses or misconfigurations begin to accumulate in your operating system.
Boot System Rescue CD.
The menu is pretty self explanatory. The only caveat is that you cannot use bz2 compression if you want to be able to retrieve your MBR and partition table from the partimage backup. In all respects the partimage archive is comparable to a Norton Ghost archive. It contains the files and the MBR and the partition table. It does not copy empty disk blocks. If you want to put the archive files on CD then you may want to limit the archive file size to 2000 blocks. Then if the backup requires more space partimage will create more 2000 block archive files.
I have used both of these methods to restore systems that I have backed up. Both methods are reliable. Partimage is a little bit less trouble to restore. After all, remember that with the tar archive file the disk partition information and MBR are inside the archive file. You have to extract them from the archive file in order to use them, then restore the archive file to the new disk, so it is one extra step to recover the system. On the other hand the tar method is quicker to do and you can perform a tar archive backup while the system is running. You can't do that with partimage.