HI, please help as I find this a bit confusing. I have a new system I built with a Sata II motherboard and have a couple of Sata II drives. Presently I am running XP64 but in Sata IDE mode. I would like to be able to use my drives to the full and I also want to install a partion with Windows 7. I do not want to run a RAID set of drives but I believe the RAID option may be the best.
A friend recently bought a new Compaq system "off the shelf" with Vista pre installed and this was set in BIOS to RAID although it only has a single drive.
Thanks in anticipation.

If you're using a Win7 install, I would go with AHCI unless you have multiple drives *AND* want the redundancy that RAID provides to protect from failure. If you're using XP (especially x64), you can get XP to install and run on an AHCI system but it's not trivial (whereas Win7 has inbox drivers that support it on most chipsets).