Your HDD's don't work in raid... You'll have to re-install all your system.
First you format your 2 HDD's that you want in raid. (raid0?)
After that, before installing anything you must activate the RAID option in the bios.
Now you should have the possibility to press ctrl + i between the end of the loading of the bios and the first try of your computer to boot on something.
You press ctrl + i and you'll have all you need to set the raid.
I think this part of the installation is approximately the same for you. I've an Asus P5E (chipset x38) and I've done that.
I'll not all explain if I'm not sure that it will be useful. All is perfectly explained in the manual.
At the start of the installation of the OS, you may need a floppy disc with the drivers as said Jevery.
If you want more details...
Good luck.