raid 0 means that 2 (or more) disks are striped with no backup (data is written in portions to each drive, and read from these the same) giving you higher disk performance but less data security (the chance that a disk fails multiplies with each disk, if that happens everything is lost)
raid 0 is fastest
another common form of raid is raid 5 where data is striped too but parity data to reconstruct data loss (due to failure of a drive) is saved on each disk (minimum 3 disks)
raid 5 is slower but safer (gets faster with every disk used, and is always faster than a single disk)
raid has advantages when it comes to disk access times/data transfer rates -
so if you are editing videos/sound use the raid as storage
a raid 0 with 3 drives should handle 2 uncompressed streams of pal video (each 25Mb/s) without problems - thats difficult if not impossible with a single drive
also you might put the windows swap file on the raid for higher performance when using a lot of ram (rendering for example)