Does anyone know a good way to back up my entire linux system to possibly one big tar file? (and will that work?)

I am wondering because if I need to repartition my system I don't want to mess up my os.

I suggest you check out Mondo Rescue ( http://www.microwerks.net/~hugo/ ). It does bascially what you've described here. Nice thing is, if you do have a dual boot system, you can backup your Windows partition as well.

It saved me once from disaster and I found it very easy to use.

I don't really see a big reason for that since I can just manually have a cron job tar and zip everything up to a nfs mount by myslef (am I missing something?)

I think mondo creates an image of a partition so that you can bring it back to the exact state it was. When you use a tar archive, and restore from it, the physical location of the files might change; e.g. a fragmented file will no longer be fragmented - if you use tools like mondo and partimage, then fragmented file will stay fragmented - which might make a difference for some things though I can't think of anything off the top of my head.

Also, when you back up your system, you should not backup from inside a running system. The system is changing constantly and your backing up is one of the changes taking place. You should do it from another installation or a live cd like knoppix.

....depends on the result you're looking for...

I prefer to make images of complete systems to avoid having to rebuild what gets broken via the file copy procedure... if you have another location (/dev/hdbx) to store an image of your entire disk then you could boot from cd and mount /dev/hdbx as /recovery and then:
dd if=/dev/hda1 of=/recovery/hda1.image

...play with skip= & count= to create 650MB image files and you can then write them to CDs thus creating your own system restore disks.

...there's a great thread post @ http://lists.jammed.com/forensics/2001/10/0076.html which explains it in simple terms...