For example with raid 0 you save a massive file on the pc, half of it will get saved on one drive the other half on the other so you have 2 drives reading and writing data simultaneously which is why it is faster. However if one of the drives goes down you will lose everything on both drives. Raid 1 is where the massive file is duplicated on both drives, so theoritically if drive 1 fails you can swap in drive 2 and keep going.
Now the bad news. Both RAID 0 and 1 have disadvantages:
RAID 0 - As stated above if one drive craps out everything is lost. Spilitting data across 2 drives doubles the probability of failure and makes figuring out which one is really bad a pain.
RAID 1 - since the data gets written simultaneously to both drives you get both drives virus infected simultaneously or both drives can get corrupted files written simultaneously or you install bogus drivers on both simultaneously, etc.
Also since both are active you use twice the power and a power supply fialure or electrical spike can trash both drives.
IMHO the above makes RAID worthless. You can get more speed out of them, but at a price.
If you want more HD speed get 1.5 gig of RAM and make a 1 gig HD cache on it.
If you want backup use CD/DVD RW daily (hourly if appropriate) and do a once a week disk image to a HD that is unplugged normally. Make sure you adaware, virus scan and defrag before imaging the program disk.