RAID or not to RAID

Im kinda new to the whole build a pc scene and have a question. Im building my own setup and was told that i should run 2 different hard drives. One for just the OS and games (WD Velociraptor 120 gb) and one for just storage and software (WD caviar green 1tb). Now my question to you is would it be better to run a raid setup or just to keep it as is?
Thanks

Also here is my prospective computer setup any suggestions would be great:
GIGABYTE GA-EX58-UD3R LGA 1366 Intel X58 ATX Intel Motherboard
Intel Core i7 920 2.66GHz LGA 1366 130W Quad-Core Processor - Retail
OCZ StealthXStream OCZ700SXS 700W ATX12V / EPS12V SLI Ready CrossFire Ready
EVGA 896-P3-1260-AR GeForce GTX 260 896MB 448-bit GDDR3 PCI Express 2.0 x16 HDCP Ready SLI Supported Video Card
G.SKILL 6GB (3 x 2GB) 240-Pin DDR3 SDRAM DDR3 1333 (PC3 10666) Triple Channel Kit Desktop Memory Model F3-10666CL9T-6GBNQ

Two seperate drives as suggested is always a good setup. I'd wait to try a RAID setup down the road if you are new to building PC's as you note and focus on building a stable machine. Parts selection looks good, have fun building it.