I've come across a good tool for backing up bootable hard disks - CasperXP [http://www.fssdev.com/products/casperxp/] will create an exact clone of a hard disk partition to another partition of the same size, including boot sectors. What that means is that if your main hard disk partition fails or corrupts then you change the bootable disk in the BIOS, and away you go working with a recent clone of your OS and programs. It costs $50 at my last check, and is worth the price tag if it saves a days work of rebuilding my system.
This could all be achieved by using a RAID array of disks with one of the parity of clone RAID setups. That though would be expensive and wouldn't work on a partition to partition basis like CasperXP does.