RAID is not required for the average gaming user.
raid is when 2 hard drives exactly the same, (in terms of model # / brand name and capacity) are networked together to form one super hard drive that runs twice as fast.
RAID is extremly fast, but also pretty expensive and complicated.
RAID requires a special controler built into your motherboard, or PCI card.
so basicly, RAID is like IDE x2
I don't know much else about raid, other than that... just stick to IDE unless you learn alot more about it.