RAID of any kinds needs to be carefully thought out. Analyze your applications. If your transcoding/encoding work already uses 100% CPU time, it probably won't benefit from RAID-0. If you frequently shuffle files back and forth, copying between two independent disks will be faster than copying within a RAID-0 array. If you are pulling stuff off the Internet, you will be limited by the speed of your intenret connection, once again no benefit to running RAID-0. If you are experiencing disk swapping, adding RAM will do more than any faster hard disk ever could hope to.
Also, installing Windows on its own drive, ideally a WD740GD or something in a similar league, and putting your media on spearate drive(s) will improve system responsiveness much more than running a RAID-0 array with everything on it.