With Raid 1, you need at least 2 drives. 1 drive is an exact copy of the other. everything writen goes on both drives. That means if you have 2 x 160Gb drives. Your total capacity will be 160gb, not 320gb. If one drive fails you have a perfect copy still there.
Raid 5 is more complicated but I'll try to explain in a fasion that's not strictly true but is close enough.
With Raid 5 you need at least 4 drives. When something is written it goes onto 3 drives (not copies). The fourth drive stores details of the files written to the other 3. This means if you have 4 x 160Gb drives your total capacity will be 480Gb (3x160). If one of the three drives fails. Using the information stored on the fourth drive you can re-create the failed drive. you have to install a new Hd of course. but it will "Like magic" be re-built from the two remaining drives and 4th.
So you have the speed of stripping (Raid 0) and Fault tollerance.
Theres also raid 1.5 in which you use 4 drives. 2 are stripped and two are mirrors. 4 x 160gb gives 320gb capacity. Speed and fault tollerance also.
Stripping is where you have say a 1gig file. it is saved to two stripped drives. It saves 64k on one drive and simultaneously 64k on the other. So theoretically the one gig file is written in half the time (512Mb on each). And when you load, it is loaded 512mb of each drive. twice the speed.
Intel Core2Duo 6400 @ 3.4Ghz
4GB Geil 6400 Ultra
3 x 500 Gb Samsung HD
EVGA 8800 Ultra OC