That's done via my motherboard's RAID controller (ASUS A8N-SLI without other stuff behind the name and is a few years old now), and since it is a fakeRAID type controller it needs additional drivers to be read by your operating system.
First I install Kubuntu Jaunty x64, using opensource software (dmraid) to control the RAID, this software was recommended by my motherboard manufacturer so it should and does work properly. Now, that was easy.

So, next thing. I decided I wanted to dualboot Windows again.
Ohh the irony, what a nightmare.
Initially I try to install Windows Vista Ultimate x64, and of course it doesn't have drivers for my RAID array to begin with so I scour the webs for drivers. I find various drivers, try them all to make setup see my RAID drive, but to no avail as it still doesn't see my RAID array - but rather two separate, unformatted harddrives. Great.
So I phone my motherboard manufacturer - where can I get working drivers for Windows Vista to use my RAID? I literally got told that "sorry, we do not support Windows Vista, try installing Windows XP".
Then I try Windows 7 x64, but it doesn't work with drivers for either Vista or XP x64 versions.
Next try is Windows XP Pro 32bit with SP2 slipstreamed in. I press F6 to load drivers, but.. lo and behold, it turns out Windows XP can only load those drivers from a 3.5" floppy drive!
Now, why is this a problem? For the simple reason that I don't have a floppy drive anymore, just like EVERY recent PC.
The moral of the story:
Windows drivers are a failure. ASUS not providing support for Vista fails at life too.