Just copy the data to another harddrive. You could use scp if the harddrive is in another computer, or just plug the other harddrive into the computer with the original.

data backups on a weekly basis. Is there a way to back it up on the original hdd? like making an iso.

Sure there is, but that's not going to protect you from hard drive failure.

PartImage is great for backup.

I also use PartImage, it's really great and it works perfectly.
I added it to Slax (along with a couple of other modules like GParted) to have a really cool LiveCD for that kind of stuff.

I use dar to make an archive split in cdrom-sized slices which I then all put on one dvd. This approach isn't very sane, but it's flexible. You never know what you will have available to restore your backup to, right?
I also sometimes make off-site backups by scp'ing my most important files to my university account.

There's split (part of GNU coreutils).

Yes, but then you would have to cat the parts together before being able to use them again. If I'm not mistaken I could copy the parts to separate CDs and let dar read them one by one. So I could retrieve important files if I'm left with an old second hand spare system without a DVD drive and without enough disk space to hold the whole archive.

You could cat all the parts and make a pipe from that to tar. Then again, that could eat a huge amount of memory.

And it's going to be damn slow if you only want to fetch a few files from your backup.