Just posting this up in case anyone else has similar problems to me.
After months of searching and trialling various drivers I finally installed Windows 7 64 onto an AMD SB750 RAID0 array of 3 1TB Seagate Barracudas.
Motherboard is an ASUS M4A79 Deluxe.
Download the SB750 AHCI Vista drivers, version 3.1.1540.61 and put them onto a USB pen.
The process that worked for me is to make sure all flash drives etc are removed from the pc.
Make sure the DVD drive is connected to the bottom flat SATA port (SATA5).
Enable RAID on SATA 1-4 and keep SATA 5-6 as IDE in BIOS.
Reboot and use CTRL-F to build raid array.
Boot from Windows disk and start Windows setup.
When you get to where you pick the installation hard drive nothing will display.
Insert the USB pen and click on load drivers.
Navigate to the driver files on the USB pen.
INSTALL THE X86 DRIVERS FIRST
This will make the array visible.
Click load drivers again and then pick the x64. (There should be two inf files now.)
Ignore the message about digital signing and carry on installation as normal.
Each time the pc restarts until you get into Windows press F8 on boot up so you can tell Windows to disable the signed driver enforcement.
Complete all Windows updates to resolve several RAID communication issues and restart.
Everything should now work fine and no needing off pressing F8 on each startup.
Hope this helps anyone who was getting fed up like me.