Alrighty, well first you need your RAID drivers. Your motherboard either came with a floppy with them already on there, or knowing Asus, they probably just put a utility on the CD that makes a floppy with the drivers on it for you.
But yeah, first you have to configure your BIOS for RAID. It should be under the option of "Configure SATA" or something along those lines. Switch that from IDE to RAID. Save and exit BIOS. Once your PC is started, hit the key needed when prompted to get into your RAID BIOS. This the BIOS after the first BIOS. So this place gives you a bunch of options for creating your array. Most RAID BIOSes are a little different; I'm used to using nVidia and Sil RAID BIOSes, but they're basically all the same. Select the option for RAID0 (Striped) and leave the stripe size at 128Kb or so. Some people say they notice a difference with a larger stripe but I think the difference is negligible. Let's face it, RAID0 isn't that huge of a performance gain in most cases. Save and exit.
If your boot order is right, the system will now run the Windows installation CD. Run it and fill out all the usual installation stuff and you will come to a screen that asks you where you want to install Winders. Your array should come up, but before you install make sure you hit the 'load driver' button at the bottom. You can use a CD, flash drive, or floppy to load the drivers. But again, knowing Asus, they have the utility that only allows you to put the RAID drivers on a floppy. So if you don't have a floppy drive you'll have to transfer the file(s) over to a flash drive and use that. Once Windows picks it up all you have to do is select and load the driver. Fill out your timezone and whatever and you are done. Good luck with your RAID config.