I currently run 2 hard drives an 80G and a 10G. the 10G one runs my OS. I have a back up of all of my files on the other hard drive.
I also have a copy of 'fast file undelete' which was one of the cover discs (you can download it from pcadvisor website (here basically). If you do lose any info run it and you can normally salvage most of your files.
To do a simple back up, open my computer, right click on the -drive and select properties - then select tools, and then "back up".
Alternatively you could simply burn most of your important files onto a CDRW.
I have lost files before through formatting, but the fast file undelete program salvaged 90% of them.
Hope this offers some reassurance