Shoutbox

If you have the money to spend on graphics, look at the NVidia GeForce 7800 series.

RAID = Redundant Array of Independent Disks.
Usually used in big corporate servers, it uses techniques such as mirroring and striping to spread data over several disks. If one of the disks stops working, the data can still be recovered from all the others.
For home use, there's not much point TBH. It's expensive, and only really useful in large arrays.