http://www.pcmag.com/art...e2/0,1759,2005592,00.asp 
about the Seagate 160 gb external hard drive as a back up.

I want to get some sort of back up other than the CDs I currently pick for my most important stuff. I only have one hard drive and thought it would be easier getting an external one rather than installing an internal one and running into issues by doing that.
I would like to have a raid1 set up but can you do that without losing info or running the risk of problems on your existing configuration?

Other thing I'm wondering about is how these external hard drives work... Don't you have to format them? DO you have to install your operating system on them?

Well this is an old post... but I'll reply anyways. You don't want a RAID1 setup with an external hard drive. You do not have to install your operating system on them. Just plug the external drive into your machine and your OS sees it as a storage device.