The ASUS website page for your mobo here
http://asus.com/product.aspx?P_ID=iRlP8RG9han6saZx&templete=2
clearly says it has RAID support built into the 6 main SATA ports so you do NOT need to buy a separate add-on RAID board unless you need special features or ultimate performance.
You do NOT have to use ALL your storage devices in RAID arrays. To be more precise, IF you want to use RAID at all on some of your SATA devices, you actually end up setting the entire SATA port control system to RAID. After that when you boot up, one of the screen prompts you will see during the boot process will tell you to press certain keys (CTRL-I, I believe) to enter the RAID utility menu - this is covered in the mobo manual, Section 4. Within that system you can Create one or more RAID arrays. For each one created you then assign specific SATA storage devices as parts of that array. Then you specify required parameters for the array and finally finish the creation process. By default, NO device is assigned to any RAID array - only the ones you specify here will actually be used as RAID components.
IF you plan to install your OS to the RAID array and boot from that array, then you have to install RAID drivers as an early step in the OS installation process. The manual covers clearly how to create and use a floppy disk (necessary if the OS you're installing is Win XP) or a USB drive (option available if you're installing Vista or Win 7) that contains such drivers. However, if your RAID array will only be used for data storage, and the boot device is NOT part of a RAID array, the driver installation does NOT have to be part of OS installation. The RAID drivers can be installed into Windows AFTER it is installed and operating, to allow it to access the RAID array created with the BIOS RAID utility.
So in your case I believe you would install the SSD drive and both WD Black HDD's and set the BIOS SATA Storage configuration (Main Menu manual Section 3.3, then Storage Configuration Section 3.3.6) to RAID. Then from the BIOS opening screen choose Boot Menu Section 3.7 to set the Boot Device Priority. My recommendation is you set the optical drive as your first choice here, the SSD drive as second, and no other options. You would Save and Exit from BIOS Setup and watch for the prompt to hit CTRL-I to enter the RAID utility. Set up and create your RAID0 array by assigning to it only the two WD Black disks and configuring them. Finish this and go back out to reboot the machine with your Windows Install Disk in the optical drive. It should boot from that optical drive and the Install process early on should ask whether you want to install extra drivers by pushing the F6 key. I don't believe you do (if you do not plan to boot from the RAID0 array) so you just proceed past this to where Install shows you the devices available for installation of Windows. I expect only the SSD drive will show here and you use that.
AFTER windows is installed and running you can use the optical disk of utilities that comes with that mobo to install all the necessary mobo device drivers and update them fully from the ASUS website. As part of that process, you also will need to install the RAID drivers. Until that step is done (and a reboot) you will not see the RAID0 array anywhere within Windows; after they are installed the array will show up in My Computer as a "normal" disk for data uses.