I'm a little confused - which onboard RAID controller are you referring to? If you can configure RAID via Crtl-G, you should be able to install OS on it - which OS are you installing? Did you load the RAID driver during OS installation?
Thanks for the response, Edward.
I got the solution to this problem from Michael in chat support.
the issue is that win2008r2 could not create or use an existing partition on the raid volume even though the partition could be created manually with win2008.
make the dvd as first bootable device and the raid as second bootable device and disable ALL other boot devices in bios.
then DO NOT insert the flashdrive with the win raid drivers until it is called for by the os.
Intel has the BEST support in the industry.