step 1 update to the latest bios on abit's website
step 2 d/l the latest highpoint raid drivers from abit website
step 3 place it on a disk
step 4 after POST it will tell you to press control-H to set the "Bios Setting Utility" which sets up the raid array
set it up (ie add drives choose striping size set one of them to boot)
step 5 change the boot sequence to add ATA RAID 100
step 6 install windows and when it asks you if you want to install a SCSI / RAID controller hit F6
step 7 load the highpoint drivers from the disk u created earlier
step 8 when it asks you to install to a drive it should show you the raid Array (ie disk 2x the size of the single HD)
step 9 install windows as normal
if you did not do this you are not in raid just using the disks as IDE drives in a non raid config
i did this just yesterday so i know what im talking about

2x WD 1200JB's in RAID 0
i just did
step 8 install windows as normal