Hi, I guess what you are saying is that you set your disks to Raid in the bios. That's not going to work properly in OS X due to lack of driver support. You either need a mac compatible add in card OR set your disks to AHCI as you have found out and format them with disk utility to software raid (which works well in OS X). This can be made bootable, but you will need to clone your system across with disk utility or Superduper and then follow some further setup procedure as described here on the forums.
OK my rig is a bit funky, I'm chain loading OS X through Grub on a separate drive. I got Grub to load Chameleon from the Boot OS X support partition, but Chameleon won't boot the mach_kernel from within the RAID set. I tried putting mach_kernel in the Boot OS X partition but then it just panics saying it can't find the kexts.
The odd thing is, I can boot into RAID by setting the boot-pid to the RAID set on my original installation and booting into that, at which point it bounces to the RAID installation, but it seems is also loading kexts from the original installation and isn't a pure RAID boot.