RAID install on an existing array using RC1 (32+64)

Here's an odd one. I've downloaded the latest RC1 nforce drivers and tried
installing both 32 and 64 bit versions of Vista RC1 (clean install) but they
show the same problem on my 4*250GB SATA RAID0 array. Motherboard is a DFI
SLI-D.

Before and after using 'Load Driver' during setup it just shows only 3 of
the 4 drives separately. The array currently has XP Pro on it as well as a
data partition, is shown as healthy and boots fine but vista only sees 3 of
the 4 drives.

It doesn't look like a driver issue as for some reason during install it
shows Disk 0,1 and 3 but doesn't show disk 2 at all. I know that the RC1
drivers are not happy running on a motherboard with mixed SATA/IDE raid
function but these problems present before selecting a RAID driver.

I'm confused as the 4 disk array boots fine into Windows XP which is
currently installed.

I've done some more troubleshooting :-

1. ran chkdsk /f on the array (took forever) - no problems
2. Ran the Samsung HUTIL on each (SP2504C) drive - no problems
3. Updated the BIOS on each drive
4. Reset the (latest) motherboard BIOS
5. Reflashed with older motherboard BIOS - same result

Vista RC1 5600 (both 32 and 64bit) still only show three drives both before
and after choosing to 'Load Driver'.

Has anyone had success with a RAID install on an existing array using RC1?