Hey.
First off, after setting up and building your RAID array (and I assume you did this through the BIOS
utility), you have to boot up from a DOS floppy that has the FDISK utility on it.
I'm assuming you have done that and your RAID is being recognized by your PC as a single drive.
Now, just to make sure you are working with the right drive, disconnect all the other hard-drives and
CD-ROM drives, but don't touch the floppy drive as you'll have to use it.
Now, boot up from a DOS (win98) floppy disk that has FDISK and FORMAT utilities on it.
Format your RAID array (as a single drive).
Shut down the PC, reconnect all the drives, and boot up (or install your OS).
However, you should have a third single drive to install your OS on (I'm assuming it's Windows)
because Windows (at least to my knowledge) does not allow an installation onto a RAID drive, as
it does not recognize it at the setup stage of the install. You will have to install the RAID drivers
that came on the CD with your motherboard or with your RAID card (is it's a separate card).