Just install OS along w the RAID drivers
, as needed. I downloaded the RAID drivers and put them on a USB drive, and installed these during the OS install.
Thus, for me it was a straighforward clean install of 7 Ultimate on my RAID setup.
I am running 3 1TB Sata II drives on RAID 5 w a Gigabyte MB. RAID was built w Intel RAID controller, set normally through BIOS, then loaded drivers in the midst of 7's custom install. Activated 7 after updates, and it has been working perfectly from day one, including through a RAID restore (I had to replace one of the HDD a couple of weeks after the build).