Do i need a seperate raid controller for raid?

Well nearly all $100+ motherboards have onboard RAID controllers...
For normal usage, you wont need a separate RAID controller...
Those are useful mainly for network storage, or other high performance apps... So for your case, the onboard RAID would suffice...

How can you answer without seeing his post ???
He has clearly said "I am building a new computer" which implies he is going to buy a new computer WITH NEW MOTHERBOARD...
So he can check out when he buys his mobo if it has RAID...

To elaborate on the second part of your question, the more drives you add to a striped array, the greater sustained throughput. But, the more drives you add, access times start degrading. And, of course, the more drives you add the higher the chance of a drive failing effectively destroying the array, more drives also use more power.
I would suggest figuring the total amount of storage space you are looking for, and buying a couple of good fast drives with fast seek/low access times that fit the bill.

They would be fine drives for a RAID 0 array. I wasn't really commenting specifically on the drives you have, just giving you a general "what to think about" scenerio.

True, Intel's RAID-drivers are very fast with the 'enable write cache' (actually a write buffer) option enabled. It does come at severe risk of filesystem corruption should your system crash or have power problems while inside windows. So make sure you backup everything you cannot miss, but that should be done always and not because you're running RAID0 now. But with the added Write Buffer, which will use your RAM memory the same way as a hardware controller with its own memory would; the first X MB are 'free' meaning they go straight to your memory and thus are very fast. This could lead to a more pleasurable experience.

But, as windows tells you the job is finished, the Intel drivers are actually still hard at work at actually writing the data to the physical harddrives. Should power fail, NTFS's journaling will not protect you against the large write buffer in the Intel drivers.

Also, Intel's MatrixRAID would make it more difficult to recover your data should the RAID itself fail (driver issues, metadata corruption, design failures). With normal onboard RAID you can always use Linux or BSD cd and recover the data by software RAID abilities of those operating systems.

Be sure to avoid JMicron, Promise FastTrak, Silicon Image and such; their RAID drivers are a joke.

nVidia is a good second onboard RAID controller. GeForce 8200/8300 (AMD) and 9300/9400 (Intel) are something i actually recommend.

The BIOS does nothing to accelerate the RAID; the actual RAID-implementation is always in the drivers, not in any onboard hardware or chipset. So its indeed an option while being inside Windows, and it will only present itself when you installed the RAID-drivers; thus it won't work on normal non-RAID disks.

See here how to enable and disable the Write Cache option:
http://www.intel.com/support/chips [...] 016454.htm